FEBRUARY 2018 - Roller Coaster WX To End February

[srainhoutx]

The Updated WPC Excessive Rainfall Outlook shifts the Day 2 Slight Risk into areas generally along and N of I-10.

[don]

Area Forecast Discussion
National Weather Service Houston/Galveston TX
344 PM CST Tue Feb 20 2018

.NEAR TERM [Through Tonight]...

Radar this afternoon has become more active from Columbus up to
Brenham/College Station to Madisonville. Based on SPC mesoanalysis
data, this activity seems to be rooted within the main moisture
axis of 1.6-1.8 inches of precipitable water. This is also where
the LLJ is the strongest with 850mb wind around 40-50 knots and
850mb dewpoints around 13-14C. This appears to be a more favored
area for convection and training of cells given the deep upper
level flow from the SW.

Upper air analysis shows a deep trough over the western U.S. with
a strong ridge in the western Atlantic. Sandwiched in between is
the Plains where the pattern is supportive of the cold front in
north Texas stalling over the area. However since there are 30-40
degree temperature drops behind the front and the shallow nature
of the front, this front will continue to push south and likely
reach the northern third of the forecast area around 12Z Wed.
Latest HRRR and WRF ARW/NMM all support this idea along with the
NAM. Synoptic models are slower to catch onto this trend. With
this shift in the forecast, temperatures will be falling behind
the front and this means the boundary will be more of a focus for
rainfall. Trends in the NAM and then the last couple of HRRR/RAP13
runs raise some eyebrows with their QPF output. If there is a WRF
model runs that lends support to these trends it might be the 12Z
WRF- ARW from Texas Tech while the NCEP WRF- ARW/NMM show less
precipitation through 12Z Wednesday.

Overpeck

.SHORT TERM [Wednesday Through Thursday Night]...

Bottom line: it`s going to rain Wednesday and then begin to taper
off Thursday. From a pattern recognition standpoint, this
forecast for the next couple of days is not that hard. Upper
levels - we have a trough out west with SW jet stream flow and an
approaching jet streak. In fact the beginnings of the divergence
from this jet streak approaches S Texas and SE Texas Wednesday
morning. Deep moisture is in place with high dewpoint air through
the boundary layer. Precipitable water values peak around 1.6 to
1.8 inches which is right at the 30 year climo max for this time
of year. In fact, the 12z CRP sounding from today had a record of
1.61 inches of PW. Now let`s throw in a 30-40 knot LLJ from the
south that lines up normal to an approaching cold front. And
that`s the last ingredient: the cold front is now expected to push
off the coast and stall so there will be lift over the front with
all the deep moisture over the region. So overall, models are in
decent agreement with this pattern going forward. The devil will
be in the details of the mesoscale. That is where the recent
12Z/18Z NAM trends along with the HRRR/RAP may be onto something
that the other models are not resolving. Mesoscale interactions
will be critical as areas of training of storms and favored areas
of convection could shift and likely shift southward from the
original threat area for heavy rainfall. The NAM in particular
shows a meso-low feature forming on the front tied to the
divergence in the jet streak. This meso-low supports heavy
rainfall farther south and a trend to monitor overnight. Of course
the NAM has a history of not performing well in convective
situations, but still a trend to watch.

Heavy rain threat still looks to be for the northern third of the
forecast area from Brenham to Huntsville northward where 2-4
inches of rain look likely through 12Z Friday or a 2 day total for
Wednesday and Thursday. Farther south looks like 1 to 3 inches
are more likely with 1 inch along the coast. This is a little
higher than yesterday`s forecast and on track from the forecast
package from the overnight shift. However there very well could be
a shift southward in the threat area. This means that the
isolated areas of 3 inches could become more common but for now
this will serve as an alternate scenario. Overall confidence
remains in the higher rainfall amounts occurring over the
northern portions of the forecast area. The main impacts will be
still street flooding in urban areas and the usual low lying
areas/underpasses. This includes rural roads in valleys or near
creeks. For more impacts see the hydrology section below.

Thursday the cold front that stalled along or just off the coast
will push back north as a warm front. This will keep rain chances
going in the forecast with mainly elevated convection. PW values
still range from 1.6 to 1.8 inches but should be decreasing
Thursday night into Friday. Upper level forcing also moves off to
the NE which may limit the extent of convection later on Thursday.
There may still be some brief periods of heavy rainfall but not
as many convective clusters moving over the region. Rainfall
amounts look to be more in the tenth to a half inch amounts on
Thursday so the majority of the heavy rainfall threat will be on
Wednesday.

Overpeck

.LONG TERM [Friday Through Tuesday]...

The warm front that will push through SE TX Thursday, will move
move well north of the region into the NE TX on Friday. Winds will
remain onshore behind this feature, allowing moisture to continue
funneling into the region. Precipitable water (PW)values will
rise back up to 1.3-1.4 inches. Therefore, showers and
thunderstorms will again be possible Friday and Saturday, with the
best coverage north of I-10 Friday into Saturday. Precip coverage
will then shift east by Saturday afternoon, with the best chance
for showers and thunderstorms east of I-45 and south of I-10.

Saturday night into Sunday morning an area of low pressure
associated with a frontal boundary tracks eastward across the
midwest. A Pacific airmass fills in behind this feature, as the
front pushes southward into the region reaching our northern zones
as early as Saturday afternoon. There is some discrepancy between
the global guidance regarding the timing of this front. The GFS
brings the cold front into the region faster than the ECMWF. GFS
also shows cooler temperatures behind the front in comparison to
the ECMWF, as drier air filters into the region. Forecast
soundings show a quick drop in PW values behind the front,
potentially falling as low as 0.4-0.6 inches according to both the
GFS and ECMWF. High temperatures behind the front will range
between the mid 60s-70s, with low temperatures in the low 50s-
60s.

Surface high pressure attempts to build back into the region
Monday into Tuesday, and a warming trend will commence.
Temperatures should rise back above normal climatological values
by the beginning of next week. Onshore flow will also return, as
winds turn out of the southeast.

Hathaway

[BlueJay]

We've got some rumbles of thunder going on up here.

[srainhoutx]

Tuesday evening briefing from Jeff:

Heavy rainfall likely tonight-Wednesday night over the northern half of SE TX.

Ingredients coming together to produce heavy rainfall across SE TX late tonight into late Wednesday night. Slow moving frontal boundary with a very significant temperature contrast of 30-40 degrees is moving southward over TX this afternoon with an extremely moist air mass with moisture levels near record mid February levels resides over the eastern half of the state. Numerous thunderstorms have developed in the favored jet regions over TX along with disturbances moving NE out of MX. One important trend today has been the large temperature contrast along the front which is helping to move it southward more than expected. Meso scale models appear to be catching on to this trend and now bring the front across SE TX and into the coastal areas on Wednesday. Feel this may shift the focus of the heavy rainfall axis southward deeper into SE TX and this trend along with model rainfall amounts will need to be closely monitored this evening and overnight.

Rainfall Amounts:
Widespread 1-3 inches of rainfall appears likely over much of the region with lesser amounts near the coast. Locations along and north of a Brenham to Conroe to Livingston line will likely see totals of 2-4 inches. Isolated higher amounts are possible across the area. Trend today has been to shift these higher totals southward deeper into SE TX and if this continues areas along and N of US 59 will need to be raised into the 2-3 inch range. Given the extremely high moisture levels in place there is certainly concern for intense rainfall rates of 1-2 inches per hour and this could quickly add up totals under any areas of cell training.

The overall meso scale pattern over the next 24-36 hours will greatly dictate where maximum rainfall totals will occur.

Hydro:
Conditions remain favorable for maximum amounts of run-off due to both soggy grounds and lack of vegetation cover. Large scale nature of this event will likely support rises on area river systems including the Trinity, San Jacinto, Navasota, and Brazos basins. It is possible that some of these basins may approach flood stage depending on how the rain falls over the next 24 hours. As for Harris County, rises on areas bayous and creeks are certainly possible, but at this time not expecting widespread overbank flooding…some of the typical trouble areas may get close to bankfull (South Mayde, upper Spring, upper Little Cypress). Main threat is for street flooding across the Houston/Harris County urban areas where rainfall rates exceed local drainage capabilities.

[srainhoutx]

Keeping a keen eye on a impressive disturbance about to cross the Rio Grande in deep S Texas. The latest HRRR guidance has initiated well with the thunderstorm complex and suggests a very stormy morning commute. Be sure to check the radar and forecast before the hectic morning rush.

[srainhoutx]

Another Tuesday Update from Jeff:

Chances for heavy rainfall increasing late tonight into Wednesday morning across the central portions of the area.

Carefully watching nose of strong upper level disturbance ejecting out of MX across S TX with rapid development of convection. Evening CRP soundings showed an incredible PW of 1.81 inches which is off the charts for this time of year and certainly with this type of moisture intense hourly rainfall rates are possible. Meso scale models are struggling with the small scale features that could result in a period of banding heavy rainfall near/around the US 59 corridor on Wednesday morning.

Widespread amounts of 2-3 inches with isolated totals up to 5 inches will be possible. Intense rainfall rates of 1-2 inches per hour or even greater will be possible which will induce street flooding in the urban areas. Significant rises on area creeks and bayous will be possible especially with short term intense rainfall rates of 3-4 inches in a couple of hours. Widespread totals of 4-5 inches over any watershed will likely result in near bankfull conditions…these amounts currently appear to be on the higher end, but given the air mass moving up the coast toward the area cannot discount totals greater than 3 inches.

It is certainly possible that the morning rush hour could be impacted.

[jasons2k]

Waco Regional is at 47F. Across the freeway at TSTC it's 72F and the wind just shifted there.

Also, lots of lightning with the storms to the SW firing up.

[don]

The NWS mentions that a Flash Flood Watch may be issued...


Area Forecast Discussion
National Weather Service Houston/Galveston TX
901 PM CST Tue Feb 20 2018

.DISCUSSION...
At 7 PM, a cold front extended from about Paris to Gateville to
Fort Stockton. Scattered showers continue to develop just ahead
and behind the front. Earlier tonight, some moderately heavy rain
fell across Walker, Madison and Houston counties with Wyser Bluff
in Walker county receiving 1.58 between Noon and 7 PM. FWIW, the
radar is underestimating precip and the gages are showing 25-35%
higher totals. At 850 MB, a 45-50 kt low level jet is located
over East TX/West LA with a ribbon of higher moisture across
central LA into central TX. At 300 mb, upper level winds show a
broad split over N-NE Texas. Water vapor imagery shows a well
defined disturbance over northern Mexico. Storms were developing
in advance of this feature and will continue to do so. Both the
GFS/ECMWF show this speed max and this feature will approach the
middle coast placing SE TX in a LFQ. Feel convection will fill in
toward the middle coast tonight and move into SE TX prior to
sunrise. The 00z CRP sounding showed a PW value of 1.81 inches
which is one of the highest values I`ve ever seen in February. The
unseasonably high moisture coupled with the approaching speed max
and a slow moving cold front should set the stage for widespread
showers and thunderstorms early Wednesday. Some of the rain will
be locally heavy. Widespread rainfall of 1 to 3 inches looks
likely over most of the region with some isolated areas receiving
between 3 and 5 inches. Since the 00z models are not all in yet,
will hold off on a Flash Flood Watch but one might be required for
Wednesday morning. Temps are tricky as well and will fall
significantly in the wake of the cold front. Have raised PoPs for
09-12z and bumped up QPF grids. Rest of the forecast is in good
shape. 43

[srainhoutx]

From Jeff:

A Flash Flood Watch has been issued for much of SE TX until 300pm this afternoon.

Heavy rainfall is developing in SSW to NNE bands across the region this morning with radar rainfall estimates of 1-2 inches per hour under the strongest cells. A strong cold front currently nearing College Station will slowly progress across the region today and add an additional focus for heavy rainfall. Given the slow frontal motion and extremely moist air mass in place bands of heavy rainfall and cell training will be possible this morning into the afternoon hours.

Widespread rainfall amounts of 1-3 inches are likely with isolated totals potentially upwards of 4-5 inches where any training becomes sustained for a period of time. Hourly rainfall rates of 1-2 inches will likely yield some street flooding. Rises on area bayous and creeks is likely with the forecast rainfall and current hydrological factors in place over the area.

[srainhoutx]

MESOSCALE PRECIPITATION DISCUSSION 0022 NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 245 AM EST WED FEB 21 2018 AREAS AFFECTED...SOUTHEAST AND EAST TEXAS...FAR WRN LOUISIANA CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE VALID 210745Z - 211345Z SUMMARY...SHOWERS AND THUNDERSTORMS SHOULD CONTINUE TO DEVELOP AND ORGANIZE INTO SMALL LINES OR BANDS IN AN UNSTABLE ENVIRONMENT AHEAD OF A COLD FRONT IN SOUTHEAST TEXAS. HOURLY RAIN RATES OF 1-2 IN/HR ARE EXPECTED WHERE THUNDERSTORMS CAN FAVORABLY TRAIN. DISCUSSION...A BAND OF THUNDERSTORMS THAT DEVELOPED ALONG THE MIDDLE TEXAS COAST HAS BECOME A LITTLE MORE EXPANSIVE AS OF 0730Z AND STRETCHED FROM NEAR BRENHAM TX TO NEAR PORT LAVACA TX. KEWX AND KCRP DUAL POL ESTIMATES HAVE RAIN RATES APPROACHING 2 IN/HR...AS DOES MRMS. THIS LARGER BURST OF CONVECTION MAY HAVE BEEN SUFFICIENT TO GENERATE A WEAK MCV PER LONGER RADAR LOOPS WHICH IMPLY A DEEPER FOCUS FOR CONVECTION AND SHOW AN EROSION OF RAIN IMMEDIATELY TO THE NORTHWEST AND WEST. THIS MCV WOULD LIKELY BE EMBEDDED ON THE NORTHERN END OF THE TRAILING STRATIFORM RAIN NEAR BASTROP TX. THE ASSOCIATED BAND OF THUNDERSTORMS WAS SITUATED ON THE WESTERN EXTENT OF A REGION OF SCATTERED SHOWER AND THUNDERSTORM DEVELOPMENT IN SOUTHEAST TEXAS IN AN UNSTABLE ENVIRONMENT (MLCAPE AROUND 1000 J/KG) ON THE NOSE OF A LOW-LEVEL MOISTURE TRANSPORT MAXIMUM. AS THE MCV SLOWLY LIFTS NORTHEAST AND INTERACTS WITH THE EXTENSIVE SURFACE FRONT...IT MAY CONTINUE TO FOCUS A TRAINING BAND OF HEAVY RAIN AND THUNDERSTORMS THAT WOULD SHIFT NORTHEAST JUST AHEAD OF THE COLD FRONT ALONG THE THETAE GRADIENT...AND ON THE NOSE OF THE STRONGER LOW-LEVEL INFLOW. ADDITIONAL TRAINING OF CONVECTION COULD ALSO OCCUR FURTHER TO THE EAST IF CONVECTIVE ELEMENTS WERE TO BECOME DEEPER AND TAP INTO THE MORE SUBSTANTIAL BOUNDARY LAYER INSTABILITY ACROSS THE REGION. HI-RES MODELS OFFER A VARIETY OF SCENARIOS AS TO HOW CONVECTION WILL EVOLVE ACROSS EAST TEXAS THIS MORNING...BUT FROM A PATTERN RECOGNITION STANDPOINT...WOULD EXPECT THE BEST CHANCE OF HEAVY RAIN TO BE FOCUSED WITHIN THE CHANNEL OF DEEP MOISTURE WHERE IT OVERLAPS WITH GREATEST BOUNDARY LAYER INSTABILITY JUST AHEAD OF THE COLD FRONT. OVER THE NEXT SEVERAL HOURS THIS WOULD BE ROUGHLY FROM NEAR COLLEGE STATION NORTHEAST TO NEAR SHREVEPORT. AS HAS ALREADY BEEN ESTIMATED BY RADAR...AND OBSERVED BY SOME MESONET SITES...RAIN RATES UP TO AROUND 2 IN/HR WILL BE POSSIBLE GIVEN THE DEEP MOISTURE AVAILABLE. THESE WOULD BE MOST LIKELY WHERE FOCUSING MECHANISMS ARE READILY AVAILABLE TO FUNNEL CONVECTIVE ELEMENTS OVER THE SAME AREAS...SUCH AS ON THE DOWNSHEAR AND SRN FLANK OF THE MCV AS IT APPROACHES THE SYNOPTIC COLD FRONT. LAMERS ATTN...WFO...CRP...EWX...FWD...HGX...LCH...SHV...

[unome]

16 at Dalhart (wind chill of 3) http://www.weather.gov/lub/

72at IAH http://www.weather.gov/hgx/

wind chimes & lightning/thunder woke me earlier, brief power outage, air dead calm now

looks like some outages in DWH area http://gis.centerpointenergy.com/outagetracker/

https://weather.msfc.nasa.gov/cgi-bin/b ... _drop=show

[srainhoutx]

Update from Jeff:

Urban Flood Advisory for SE Harris County and Galveston County until 515am.

Band of heavy rainfall producing 1-2 inches per hour from Pasadena to League City. HCFCD gage has recorded 1 inch of rainfall in 30 minutes over Beamer Ditch near the south Beltway. Additional rainfall of .5 of an inch of rainfall will be possible over the next 30 minutes.

Additional showers and thunderstorms over Matagorda and Brazoria Counties will lift NNE toward SW Harris County over the next 1-2 hours.

[snowman65]

We have been finally getting the weather we were supposed to have all winter because of la nina (temp wise, anyway). We had a surprisingly cold and "snowy" winter, but now it's time to pay the piper. Party's over....lol.

[srainhoutx]

Cold front continues to advance S across SE Texas. Currently the frontal boundary is South of Brenham and Huntsville. It's 49Fin Brenham and 73F in Angleton/Lake Jackson. Take a jacket today. You'll need it if your headed into town.

[tireman4]

000
FXUS64 KHGX 211152
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
552 AM CST Wed Feb 21 2018

.AVIATION...
We`re starting to see a break in the precip as a upper level
disturbance departs to the northeast. But suspect the break is
just temporary as returns are starting to reappear along the
frontal boundary in the Hill Country. Think this precip will
eventually fill back in. Front has pushed south of CLL and should
make it fairly close to the coast toward sunset. A mix of MVFR/IFR
ceilings and visibilities will persist (IFR will dominate behind
the front). Still concerned about locally heavy rain along/south
of the front. 47

&&

.PREV DISCUSSION... /ISSUED 431 AM CST Wed Feb 21 2018/
Showers and thunderstorms continue to develop across Southeast
Texas early this morning and move rapidly off to the north and
north northeast. This fast motion has been keeping peak rainfall
rates (according to some Harris County Flood Warning System gages)
at around 1 to 2 inches per hour, and a couple gages between
Houston and Katy already have totals over 2 inches. The potential
is there for additional activity to develop during the day today
as a slow moving cold front currently across our N and NW counties
possibly becomes a focus as it works its way toward the coast. It
is possible that activity will continue to move fast enough to
keep rainfall totals below area flash flood guidance values
(generally around 2.5 to 3.5 inches in 1 and 3 hours and 3.5 to
4.5 inches in 6 hours), however very high and near record
precipitable water values ahead of the front in combination with a
30 to 40 knot low level jet and ejecting shortwaves/impulses
moving across the area in the deep southwest flow aloft could
bring additional rounds of showers and thunderstorms to the area.
The stronger activity or where any training sets up has the
potential to produce higher rainfall rates (1 to 3 inches per hour
with locally higher amounts) that could lead to flooding, and
have gone ahead and issued a Flash Flood Watch for much of our
area through this afternoon (WPC does have most of our area in a
slight to moderate risk for excessive rainfall today). It is also
quite possible that the cold front could stabilize a large part of
the Watch area to prevent any significant additional development.
We will likely need to do some Watch reconfigured during the day
as we see whether or not additional heavy rains do develop. 42

MARINE...
Winds have diminished, but lingering 4-6 foot seas remain so will
maintain the caution flags offshore. Visibility is all over the
place in the nearshore waters (fine where there`s precip, but some
dense fog elsewhere). Will also maintain the ongoing dense fog
advisory for the nearshore waters. Cold front is forecast to sag
close to the Houston Ship Channel-Matagorda Bay prior to
sunset...then likely stall along the coast before moving back north
on Thurs. Fog will be an issue in the warm sector through
tonight...then persist until the next front moves off the coast late
Sat. 47

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 56 39 56 51 73 / 90 70 60 50 50
Houston (IAH) 74 54 69 64 76 / 90 70 60 30 30
Galveston (GLS) 72 61 68 64 71 / 70 70 40 20 20

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Flash Flood Watch until 3 PM CST this afternoon for the
following zones: Austin...Brazos...Burleson...Colorado...
Fort Bend...Grimes...Harris...Houston...Liberty...Madison...
Montgomery...Polk...San Jacinto...Trinity...Walker...
Waller...Washington...Wharton.

GM...Dense Fog Advisory until noon CST today for the following zones:
Coastal waters from Freeport to the Matagorda Ship Channel
out 20 NM...Coastal waters from High Island to Freeport out
20 NM.

SMALL CRAFT SHOULD EXERCISE CAUTION until noon CST today for the
following zones: Waters from Freeport to the Matagorda Ship
Channel from 20 to 60 NM...Waters from High Island to
Freeport from 20 to 60 NM.

&&

$$

[tireman4]

Differences in Temperatures at 8:15 am

[tireman4]

Front Placement as of 8:15 am

[Belmer]

Here in Pasadena, woke up to some of the loudest thunder I have heard in a long time. Felt like CG lightning was hitting everywhere around my house. Woke up around 3:45 this morning to car alarms going off in my neighborhood.

[srainhoutx]

The front is passing through NW Harris County at this time. Temperature has dropped into the low 60's and falling.

[tireman4]

Srain is right, the temperature difference is stark...