December 2016- End Of Year Forecast

[unome]

the uncertainty in the models makes it a good time to pay close attn to local forecasters, looking forward to later discussions:

http://www.weather.gov/hgx/
https://www.facebook.com/NWSHouston
https://twitter.com/nwshouston

https://twitter.com/iembot_hgx

The cooler/drier weather in the wake of this front for Weds/Thurs is expected to come to an end Friday. The return of onshore winds and low-level moisture will be setting the stage for a wet/active weekend. A deep closed upper low/trof (developing in the vicinity of the California Baja) is progged to move east across nrn Mexico Sat/Sun with a coastal surface trof setting up over the middle to lower TX coast out ahead of it. These systems combined with possible PWs near 2" are all pointing to widespread unsettled weather for most of the weekend with heavy rain as the main issue. Models appear to be in slightly better agreement with these runs, but we are still seeing the biggest differences with timing. So for now, stay tuned. Will be adding some initial wording for this weekend in the HWO later this morning.


http://www.wpc.ncep.noaa.gov/index.php#page=frt

[srainhoutx]

Tuesday morning briefing from Jeff:

Significant rainfall event increasingly likely this weekend over SE TX.

Surface boundary stalled along the US 59 corridor yesterday evening and has returned slowly northward overnight in response to an incoming short wave over the Rockies. South of this boundary dewpoints are in the 70’s while north of the boundary dewpoints are in the 40’s and 50’s and this has resulted in widespread dense fog near the boundary. Recently radar has shown a few showers starting to develop over the region and this will continue through the morning and into the afternoon hours with modest heating along the boundary and a secondary stronger incoming cold front. Any severe weather should be east of the area…but a thunderstorm or two will be possible today.

Cool and dry across the region Wednesday-Friday with lows in the 40’s and highs in the 60’s.

Weekend:
A powerful upper level storm system will drop into the SW US/N MX late this week and slow down this weekend. Increasing SW flow aloft will help to foster the formation of a surface coast trough from the upper TX coast to the lower TX coast where surface convergence will be maximized. NE surface winds will lock in cold surface temperatures in the 40’s and 50’s while a few thousand feet off the ground warm moist southerly flow will overrun the surface cold dome…the result will be widespread rainfall…some heavy.

While models continue to disagree on the timing of this feature with the GFS/CMC/UKMET the slowest and the ECMWF the faster…the all agree that some significant QPF is looking likely with this event. The GFS has been producing 3.0+ inches at BUSH IAH for the last several runs in a row. Given forecasted PWS approaching an extremely high 2.0 inches feel the threat for heavy rainfall is growing for this weekend. Main question is does the active convection focus near the surface trough off the coast or in an elevated fashion inland of the coast. Both are possible at this point…but the results would be vastly different QPF.

For now will go with widespread rainfall of 2-4 inches starting late Friday and lasting into Monday with isolated amounts of 6 inches possible. This is falling in line with current WPC forecasted amounts. Should the coastal surface trough back northward or form closer to the coast this would increase the threat for prolonged cell training of heavy rainfall.

The entire period will be cold with temperatures hovering in the 40’s to lower 50’s much of the weekend as NE surface winds drain cold air into the region under rain and clouds.

Gatlinburg/Pigeon Forge Wildfire Complex:

An incredibly devastating night for the resort areas of eastern TN as at least 14 wildfires driven by 50-70mph winds burned through Gatlinburg, Sevierville, Kodak, and Pigeon Forge/Dollywood. The magnitude of the fire that swept across this area yesterday afternoon and evening is rare for the eastern US. This exact event is what has been feared for so many weeks as crews have battled to gain control of the many fires burning in the Great Smokey Mountains in fear that weather conditions would change rapidly (as is normal for this time of year) …yesterday was that day.

The same low level jet that was roaring overhead of SE TX yesterday moved over E TN late yesterday afternoon with frequent surface wind gust of 50-70mph. Fires that had been burning in the Great Smokey Mountains to the south of Gatlinburg for weeks exploded even with RH values of 50% or higher being driven by intense surface winds. At 400pm the fire complex was nearing Gatlinburg from the SE/S/SW.

Between 400pm-1100pm the wildfire erupted into a firestorm with forward burn rates of nearly 50mph at times racing the fire northward through large sections of Gatlinburg and into Pigeon Forge. Crews working fire lines to protect the towns during the day were rapidly overrun and tremendous spotting of embers in the strong winds resulted in the initial fire expanding into at least 14 different fires in the matter of a few hours. Air support was grounded due to the strong surface winds and ground crews Fire rapidly overran the primary evacuation route out of Gatlinburg…see images below. Visitors in many of the areas hotels were trapped in the hotels as fire rapidly surrounded many of the structures.

Radar data showed nearly 45dbz in the smoke plume indicating large amounts of ash and objects were being lofted into the air suggesting the fire had developed surrounding inflow winds and strong center updrafts…something only seen in the most intense of wildfires. To give a picture of how quickly the fire evolved attached is a weather station in Gatlinburg which was overrun by the fire. The surface temperature spiked to 118 degrees and the RH fell to 21%...clearly the fire was creating its own weather as other sites nearby were reporting 50-60% RH values. Also note the peak wind gust of 69mph about 2 hours before the site was overrun…showing intense surface winds near the fire line. Note the inside structure temperature was 64.9 degrees…clearly the fire was advancing on the structure at this moment…and this was the last report from this site.

11292016 Jeff 1 untitled.png (119.92 KiB) Viewed 4851 times

Officially 100 structures were lost in the areas surrounding Gatlinburg and Pigeon Forge including a 16 story hotel, but the scope of the devastation will not likely be known until today when the sun rises…some estimates suggest nearly 1/3rd of the town of Gatlinburg burned overnight. As one meteorologist said this morning “not since the Great Chicago Fire has a combination of weather events, combined to cause such an event east of the Mississippi River”

Evacuation Traffic Being Overrun by fire on HWY 441

Wind driven spot fire on primary evacuation route out of Gatlinburg…HWY 441

11292016 Jeff 3 untitled.png (246.68 KiB) Viewed 4851 times

Downtown Gatlinburg:

11292016 Jeff 4 untitled.png (209.18 KiB) Viewed 4851 times

Fire advances on Gatlinburg out of the mountains

11292016 Jeff 5 untitled.png (245.76 KiB) Viewed 4851 times

Gatlinburg:

[MontgomeryCoWx]

12z GFS brings quite the Arctic blast early next Thursday morning.

Would not get out of the 30s in MoCo on Thursday followed by a couple of freezes.

[srainhoutx]

12z GFS brings quite the Arctic blast early next Thursday morning.

Would not get out of the 30s in MoCo on Thursday followed by a couple of freezes.

Looks like the first true "Bue Norther" we have seen in a couple of years. We will need to watch the Winter Storm that develops to our S and W and moves into the Plains laying down a bunch of snow. If we see significant snow cover develop across the Central and Southern Plains, that tends to suggest less in the way of airmass modification for any future cold air intrusions. Stepping down...

[srainhoutx]

The 12Z GEFS Ensemble Mean agree with the other guidance suggesting the first real shot of Arctic air surges South late next week.

Still looking raw, stormy and wet this coming weekend.

[srainhoutx]

the 12Z ECMWF suggests a bit slower ejection of the cold core upper low this weekend and has trended toward the slower and deeper solutions with the trough to our West. That would mean the heavy rainfall potential could increase a bit with better agreement with the other guidance and the ECMWF shows a developing Coastal trough/low as well.

The attachment 11292016 12Z EC 120 f120.gif is no longer available

In the extended range, the "Blue Norther" is still showing up very well for arrival a week from tomorrow.

[srainhoutx]

The weekend forecast is becoming increasingly worrisome, but at this range still lacks confidence. The Global Models and their ensemble members have come into better agreement regarding the very deep trough that looks to settle well into Mexico near or just East of the Baja Peninsula. A very potent cold core low at the 500mb level is expected to deepen over Mexico and tap a very noisy sub tropical Jetstream with abundant tropical moisture at the mid and upper levels reaching back to near Hawaii. That moisture appears to have several embedded disturbances that will round the base of the deep trough with a couple of shortwaves dropping S along the Western flank of the trough along the Washington/Oregon/California areas adding some energy to the potent cold core low. Overrunning precipitation is expected to develop atop a shallow cold airmass at the surface Friday night into Saturday with a strong SW flow aloft. The reliable models have agreed today that a Coastal low/trough could organize near Brownsville to Corpus Christi with the potential of a Coastal low developing Saturday night into Sunday and possibly next Monday. Elevated thunderstorms are possible Saturday night into early Monday as the Coastal low moves along the Upper Texas and SW Louisiana Coast. The upper low looks to begin shearing out Sunday evening into Monday as it moves across Texas. The afternoon Update 7 Day Quantitative Precipitation Forecast suggest bouts of heavy rainfall may be possible, particularly along and offshore of the Texas Coast. This is a very complicated and challenging forecast, so expect changes as we near the end of the work week.

[DoctorMu]

Freezing down to the HOU area next Friday am (Dec 9)...off in fantasyland. Waiting for 18z run to complete.

[MontgomeryCoWx]

Long range keeps reloading cold air in our source region and putting it on the shot block down to our smiling faces

[Andrew]

Looks like an active period for SE Texas will occur over the coming weeks. The cutoff low/coastal low combination this coming weekend looks tricky as it will be a battle between the upper dynamics to the west and the coastal low to the east. On multiple occasions we have seen the coastal low "steal" much of the moisture that would make it more inland. As it stands right now I do expect locations along the coast will see highest totals and a relatively sharp gradient will exist as we move inland. With that said, the ECMWF is more encouraging with moisture streaming further inland (less influence from the coastal low) and isolated totals reaching 5-7 inches inland. Overall though much needed rain looks to occur for most across the region.

Next, the artic outbreak is looking more and more likely for the December 9th timeframe as both global models continue to keep the AO in a negative state. The ECMWF is most aggressive with the colder air showing dewpoints reaching close to the single digits over parts of SE Texas. The GFS keeps dewpoints in the mid to upper teens though. Still a longways out and modification and proper adjustments will need to be made.

[Electric Lizard]

This morning's NWS disco gets on board with next week's cold by suggesting a bear watch may be warranted soon.

[srainhoutx]

Wednesday morning briefing from Jeff:

Wet weekend for much of the state

Same cold front responsible for the 23 tornadoes overnight in LA, MS, AL of which one struck a 24-hr daycare at 213am this morning completely destroying the structure and critically injuring four children and resulting in 3 nearby fatalities, has pushed off the TX coast allowing a refreshingly dry air mass to overspread the region.

Cold air advection will continue today with temperatures slowly falling this morning into the 50’s across much of the entire area under N winds and a mid level cloud deck. Highs will only reach the mid to upper 60’s today compared to the record breaking mid 80’s on Tuesday. Coldest morning will be Thursday under clear skies and light winds and expect temperatures to fall into the upper 30’s NW to near 50 at the coast.

Friday-Sunday:
While there are still timing differences on when this weekend storm event will begin and end…models remain in good agreement that a very wet pattern will develop over SE TX.

Friday:
An upper level storm system will move from the NW US southward into NW MX and begin to cut off from the main jet stream flow aloft. The deep southern position of the upper level trough will begin to force surface pressure falls along the lower TX coast late Friday. Moisture will rapidly return across TX from both the Pacific and the Gulf of Mexico starting on Friday and we may begin to see showers break out by late Friday afternoon…which is a little faster than the previous thinking. Developing coastal low off the lower TX coast will lock in cold NE surface winds and cold air mass over the region with mid level moisture spreading northward over this surface cold dome.

Weekend:
SW flow aloft on the eastern flank of the NW MX upper level storm system and developed/NE tracking costal trough/low will result in messy conditions for the weekend. Strong overrunning of warm moist air above the surface cold layer will result in widespread rainfall from Saturday morning well into Sunday night and likely into Monday. Rainfall, clouds, and NE wind draining cold air in to the region will keep a near steady temperature through the entire period in the upper 40’s to mid 50’s.

Current thinking is that the coastal trough/low will progress from the lower TX coast late Saturday NE/ENE to off the upper TX coast by early Monday which will bring some marine impacts to winds and possibly tides. This track of the surface features and warm/cold sectors of the storm system favors the maximum rainfall totals to be along the coast and offshore as well as any severe weather threat. Should the surface low track inland or closer to the coast higher rainfall totals and severe weather would need to be added likely for Sunday.

Rainfall Amounts:
Widespread rainfall amounts of 2-4 inches are likely over the next 5 days with most of this falling Saturday and Sunday. Expect the 2 inch totals more inland with the higher totals near the coast and offshore. Could see isolated amounts upwards of 6-7 inches over the coastal waters given forecasted PWS of 1.7-1.9 inches. Certainly the threat for heavy rainfall is there with those kind of PWS values, but current thinking is that the most concentrated convection will remain along and SE of US 59. Should the coastal trough track closer to the coast or slightly inland then rainfall amounts will need to be increased along and S of the US 59 corridor.

5-Day Forecasted Rainfall Amounts:

Cold Air Outbreak:
Bitter cold air mass which has been stuck in Russia and Siberia for much of November has built into Alaska over Thanksgiving where current temperature readings are in the -30F to -40F range. Both the ECWMF and GFS along with several of their ensemble members develop an increasingly amplified upper air pattern next week over the northern Pacific which forces high pressure to build northward toward Alaska and then a deep downstream trough to form over the western US. This is certainly an upper level pattern favorable for delivery of a cold source region (Alaska) arctic air mass southward into the US. Given that the source region is actually fairly cold and expected to remain cold adds support to a significant intrusion of cold air into the plains by the middle to end of next week. [/i]

[srainhoutx]

Some have been asking what the mid December toward Christmas timeframe may offer. The Updated CFSv2 Monthly climate model suggests colder than normal temperatures and slightly above normal precipitation chances. Typically I have noticed a bit of a warm bias for this particular Long Range Ensemble Model over the years. That said look how cold our source Regions of Eastern Alaska and NW Canada throughout the month.

[srainhoutx]

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1100 AM EST WED NOV 30 2016

VALID 12Z SAT DEC 03 2016 - 12Z WED DEC 07 2016


...OVERVIEW...

ONCE AGAIN...THE MEDIUM RANGE PERIOD (SATURDAY THROUGH WEDNESDAY)
CONTINUES TO BE PLAGUED BY THE UNCERTAINTY OF THE UPPER TROUGH
EJECTING EASTWARD FROM NORTHERN MEXICO. HOWEVER...ENSEMBLES ARE
BEGINNING TO COME TO A CONSENSUS REGARDING ITS EVOLUTION. BY DAYS
6 AND 7...THERE CONTINUES TO BE AGREEMENT AMONGST THE MODELS WITH
THE INCOMING DIGGING TROUGH FROM THE PACIFIC.


...MODEL EVALUATION/PREFERENCES...

THE BIGGEST CHALLENGE IN THE FORECAST ONCE AGAIN IS THE TRACK AND
SPEED OF THE UPPER LOW OVER NORTHERN MEXICO ON SATURDAY. THE GFS
CONTINUES TO HAVE GOOD CONTINUITY WHILE THE 00Z ECMWF BEGAN TO
MIRROR THE OLDER MODEL RUNS OF BEING TOO FAST ALONG WITH THE
ENERGY FROM THE NORTHERN STREAM STACKING ON TOP OF THE CLOSED LOW
OVER MEXICO. THE 00Z GFS AND GEFS BOTH SHOW THE NORTHERN STREAM
QUICKLY PROGRESSING TOWARD THE EASTERN US AS THE UPPER LOW OVER
MEXICO SLOWLY TREKS TOWARD TEXAS OVER THE WEEKEND. HOWEVER...THE
ECMWF ENSEMBLE MEAN BEGAN TRENDING TOWARD THE GFS/GEFS SOLUTION
WITH THE PLACEMENT AND TIMING OF THE UPPER LEVEL LOW AND BY
MONDAY...THE UPPER LOW WEAKENS OVER TEXAS AND TRACKS EASTWARD.
BECAUSE OF THIS...USED A 00Z GEFS/GFS/ECENS BLEND BUT LEFT THE 00Z
ECMWF OUT DUE TO IT REGRESSING BACK TO ITS OLDER TRENDS.

BY DAYS 5 THROUGH 7...GOOD AGREEMENT REMAINS ON THE ENSEMBLES
SHOWING A RIDGE BUILDING ACROSS THE GULF OF ALASKA...WHICH WILL IN
TURN ASSIST IN ANOTHER UPPER TROUGH DIGGING ACROSS THE WESTERN US.
THIS UPPER TROUGH WILL PROGRESSES QUICKLY ACROSS THE CENTRAL US
BY THE END OF THE MEDIUM RANGE PERIOD. MEANWHILE...THE RIDGE WILL
BUILD BACK ACROSS THE WESTERN CARIBBEAN AND SOUTHEAST.


...WEATHER HIGHLIGHTS/THREATS...

THE POTENTIAL FOR HEAVY RAIN ACROSS THE EASTERN HALF OF TEXAS AND
THE LOWER MISSISSIPPI VALLEY REMAINS FOR THIS WEEKEND AS THE UPPER
LOW MOVES OVER THE REGION. AT THE SURFACE...A LOW WILL TRACK
ACROSS THE WESTERN GULF OF MEXICO AND MOVE NORTHWARD ACROSS THE MS
VALLEY. IN ADDITION...VALLEY RAIN AND MOUNTAIN SNOW WILL SPREAD
ACROSS THE PACIFIC NORTHWEST AS A SURFACE FRONT MOVES ACROSS THE
AREA. SNOW WILL CONTINUE ACROSS THIS REGION IN ADDITION TO THE
NORTHERN ROCKIES AS MOIST ONSHORE FLOW CONTINUES UNDER A STRONG
WEST-EAST UPPER LEVEL JET.


EXPECT BELOW AVERAGE TEMPERATURES FOLLOWING NEAR THE CLOSED LOW IN
THE SOUTHWEST/FOUR CORNERS REGION FRIDAY INTO THE SOUTHERN PLAINS
AND SOUTHEAST THIS WEEKEND. AS THE CANADIAN HIGH SPILLS OVER THE
INTERMOUNTAIN WEST BY DAY 6...MUCH COOLER TEMPERATURES WILL FILTER
ACROSS THE WESTERN US...WITH TEMPS 15-25F BELOW THE AVERAGE. THE
EAST WILL SEE A WARMING TREND AS THE UPPER RIDGE BUILDS IN FROM
THE SOUTHEAST.


FANNING

[srainhoutx]

Michael Ventrice ‏@MJVentrice · 21m21 minutes ago  Andover, MA
Big cut-off low to impact the South this weekend could produce some very heavy rains across Texas; Newest ECMWF putting out 3-6" thru Monday

[DoctorMu]

Bullseye on Galveston for the weekend rain.

[srainhoutx]

The afternoon Updated Climate Prediction Center Outlooks for Day 6 to 10 and Day 8 to 14 suggest below normal temperatures will spread across the United States.

[jasons2k]

Euro and GFS sure look different on rainfall placement.

[srainhoutx]

The overnight updated quantitative precipitation forecast and the excessive rainfall outlook suggest we may have some issues across the Eastern half of Texas extending into Louisiana.

[unome]

The overnight updated quantitative precipitation forecast and the excessive rainfall outlook suggest we may have some issues across the Eastern half of Texas extending into Louisiana.

the very soggy day 3

the closed mid level moves slowly east to western mexico during day 3. the low level inflow increases to about 30 knots from the southwest... continuing to funnel 1.75/2.00 inch preciptable water air across eastern tx into portions of la. while there is some spread on the placement of a frontal boundary extending from low pressure over far south tx... the low level moisture and marginal to locally moderate instability becomes focused on the front... increasing the threat for heavy to excessive rainfall. an axis of 2.75 to 3.50 inches of qpf was stretched from the middle tx coast across northern la and far southern ar... where the best instability is expected.

these qpf amounts are lower than the maximum qpf amounts from the 00z gfs (and even the 00z ecmwf). locally higher amounts are possible... as corfidi vectors become better aligned with the mean 850-300 mb flow ahead of the closed mid level system. members of the 00z gefs and 12z ecmwf ensemble output suggest that potential for 4.00+ inch qpf amounts... mainly over the upper tx coast into northern la. three hour flash flood guidance values are generally 2.50 to 3.50 inches... and given some of the qpf amounts from the 00z model suite... as well as the potential for training in a high moisture content airmass... a slight risk area was placed over much of eastern tx... the eastern half of la and southernmost ar for day 3.