April 2015: Pleasant Weather To End April

[Andrew]

I hope everyone is enjoying/enjoyed the cooler air, because major changes are on the horizon later this week into the weekend. First off, a relatively sharp trough is expected to deepen off the northwest coast earlier this week as a rather potent shortwave rotates around it later this week. Models are coming into better agreement that a rather large severe event could be possible from Tuesday through Thursday across much of the central and southern plains. As this embedded shortwave rotates eastward, multiple areas of cyclogenesis are expected to occur over the Texas Panhandle/ Oklahoma/ Kansas region. Paired with this, a strong 850-950mb LLJ from the gulf should usher in deep gulf moisture all the way into the northern plains. Currently off the coast of Texas dewpoints sit in the lower 70s and this air is going to advect northward at a fast rate as 50kt winds carry this deep moist gulf air far north. Expect rounds of severe weather across much of the central plains as CAPE values extend into the 3000-4000 J/kg range much of the week. Furthermore, cyclogenesis should backen winds at the surface through a large portion of Oklahoma, Kansas, and Arkansas with strong vertical veering expected. Helicity values of 500-600 will be possible across much of this area. Currently the 00z NAM shows EHI values ranging in the 11-12 range for Wednesday evening! As it stands now this is expected to be one of the bigger events in recent history and you can see that in the wording from the SPC. While models differ on the timing and intensity of the front late Thursday evening, both the GFS and ECMWF show a line of storms moving through at least the northern half of SE Texas on Friday. As of now, winds and isolated hail look to be the main threat locally, but it is still too early to tell (since timing and location of the deepening central plains low is key).

The "real" event for this area is looking more and more like it will occur next weekend as another deepening trough off the west coast is accompanied with a rather potent cut off baja low. The GFS and EURO differ dramatically with ejection of the baja low and phasing between the longwave and baja low could make all the difference. The GFS has been trending towards the ECMWF solution of ejecting the low faster and in better phase with the longwave. If this occurs, a severe outbreak COULD occur over parts of Texas late into the weekend (Sunday timeframe). That will be something we will need to watch for as we head into the middle of the week, but expect the SPC to start mentioning it in the 4-8 day discussion with 15 or 30% probabilities possible. All in all it will be an active week for many across the central and southern U.S. as severe season has returned in full force.

[tireman4]

Great overview as usual Andrew. Thank you so much

[Katdaddy]

Its a warm muggy morning as GOM inflow begins to increase helping to enhance severe weather across the Plains. By Wednesday night thunderstorms chances begin increasing across SE TX with the weekend looking wet and potentially stormy.

[srainhoutx]

After a quiet and benign weather pattern the past couple of weeks we are beginning to transition to a bit more active pattern. For the most part our sensible weather will consist of a fast zonal flow off the Pacific across the Southern United States with a rather active Polar jet that has retreated N across Canada and the Northern Plains. The persistent eastern trough that has plagued the Lower 48 most of the late Winter/early Spring is about to transition to that of a Western trough allowing storm systems to dig S into the Pacific NW and California. The first in a series of storm systems is spinning off the Northern California Coast this morning and will begin to trek inland and ENE setting the stage for severe weather across the Plains and the Great Lakes Region tomorrow into Thursday. This storm system will carve out a trough across the West allowing a Pacific cold front to slowly advance S into our Region Thursday into Friday and stall somewhere near or just S of the I-35 Corridor of Central Texas. PW's continue to increase each day as rich tropical moisture near or above 2 standard deviations above normal become established across the Southern half of Texas into Louisiana.

By Friday a second storm system begins to dive further S along the West Coast and move inland near San Diego. As this storm system moves across Northern Mexico over the weekend and begins to turn NE Sunday, the guidance is beginning to suggest the mean trough axis could take on a more negative tilt meaning strong to severe storms begin to increase across Texas beginning Saturday and increase in areal coverage on Sunday into Monday. Very high moisture valves with veering winds across the multiple levels suggest some potential for rotating storms particularly Saturday afternoon along a dryline across West Central Texas. Storms are expect to organize across the high Plains of the Sierra Madre front range just West of South Texas and spread NE. Andrew will be following the late week into the weekend weather very closely, so be sure to check in as we get a bit closer to the late week timeframe for his in-depth analysis of this potentially very active weather pattern.

[BlueJay]

BIG shoes to fill for Andrew! He can do it. I will definitely stay tuned.

[Andrew]

Complicated setup continues to take shape over much of the central plains. Currently, the trough that we have mentioned much this week has finally come onshore over the California coast and will slowly eject towards the southeast and then eastward over the northern plains. Strong and deep moisture advection from the gulf continues tonight and tomorrow as dewpoints rise into the 60s across much of the central U.S. Over the last couple of days, many locations over Oklahoma have seen CAPE values in the 3000-4000 J/kg range and this should continue tomorrow and Thursday. The largest difference tomorrow will be the injection of a shortwave along the synoptic flow. This should provide enough lift that capping shouldn't be an issue. Furthermore, strong cyclogenesis over NW Oklahoma will help to backen surface winds and amplify the nocturnal LLJ tomorrow evening/night. Combine all this and you have EHI (energy helicity index; a measure of the CAPE and corkscrew spin in the atmosphere) values ranging in the 6-10 range. Hodographs are wide sweeping and 0-1km shear is relatively impressive. As long as early morning convection doesn't stabilize the atmosphere too much, expect strong storms to affect much of the central plains all the way down to parts of the Texas Panhandle/west Texas. As we move into Thursday, models differ slightly on how fast the trough and surface low ejects to the northeast, but the general consensus is that strong enough lift should be present for a line to develop late in the day Thursday and progress southeastward through the overnight hours. The largest difference in models from earlier this week is the washing out of the front. The current consensus is for the front to washout from the DFW area down into the College Station region. This will keep rain chances in the forecast for much of the weekend as another cut off low/ shortwave approaches from the Baja region and brings yet another chance of severe weather on Saturday and Sunday. Unfortunately the consensus from global models is very low at this time so we will have to wait and see on that aspect of the forecast.

[srainhoutx]

As Andrew pointed out, the parameters for potentially strong to severe storms are slowing increasing particularly during the Thursday night into Friday timeframe. The latest guidance suggests that an uncapped atmosphere with a rather impressive jet streak out of the Eastern Pacific crossing Mexico into Texas and Louisiana could develop with veering winds as well as a lower level increasing flow off the Western Gulf combining with a very moist and unstable airmass along and S of the stalled front typically spells an active weather pattern. The Storm Prediction Center has issued a Slight Risk for Severe Storms Thursday night into Friday with damaging wind and hail being the primary threat at this time.

[Katdaddy]

On this travel day to National Tropical Weather Conference, 3 days of active severe weather begin across large portions of the US. Texas will also be threatened with severe weather during the next 2 days. The severe weather threat will extend across N Central, N and NE TX on Thursday and then across S, SW , Central, S Central and SE TX on Friday. A wet and stormy weekend shaping up for SE TX with the flooding potential increasing Sunday into Monday with additional storm development and heavy rain with the second trough.

The Houston-Galveston NWS summarize the next several days into the weekend quite well. From this morning's AFD:

FROM MID-WEEK WARMTH IN THE 80S AND HIGH HUMIDITIES TO WHAT APPEARS TO BE A VERY WET LATE WEEK/WEEKEND...EARLY SPRING 2015 IS FORECASTTO BE ACTIVE!

[texoz]

It's been a while since I've said this, but thanks to Andrew, srainhoutx and everyone else that contributes to the weather updates. I've got two kids that play outdoor sports so getting these updates are a big help.

[srainhoutx]

Morning briefing from Jeff:

After a couple of dry weeks…two storm systems will affect the area late this week and this weekend…both severe weather and heavy rainfall will be possible.

Onshore flow continues to stream moisture inland off the Gulf of Mexico this morning with dewpoints running in the upper 60’s and lower 70’s. Zonal flow aloft with strong capping overhead will negate any rainfall chances today and for the first half of Thursday with partly cloudy skies and breezy conditions.

Thursday-Friday:
First upper level storm system ejects out of the SW US and toward the central plains with a trailing cold front moving into the area late Thursday and on Friday and stalling. Air mass south of this front Thursday afternoon becomes moderately unstable with forecasted CAPE values of 1500-2500 J/kg and steepening lapse rates aloft. Surface heating into the mid 80’s will help to erode the weakening aping inversion and expect at least isolated storms to develop along the front. Any storms that develop will pose a hail and damaging wind threat with the best chances from College Station to Lufkin Thursday evening.

Front sags southward on Friday and expect another active convective day Friday afternoon. Weak short wave will cross the area in combination with the surface front likely producing scattered thunderstorms in the heat of the afternoon. Guidance is really pegging Friday afternoon/evening to be fairly active. Again the air mass will be fairly unstable and strong to severe thunderstorms will be possible. Shear profiles are not overly favorable for tornado production, but large hail and wind damage appear the main threats. SPC has already outlooked much of the area for a slight risk of severe weather Friday afternoon.

Saturday:
Front remains stalled across the region and this will linger thunderstorm chances all day Saturday. Think the best chances will be in the afternoon hours with surface heating, but much of this depends on how much development there is Friday afternoon and if the air mass is “worked over” and needs time to recharge.

Sunday/Monday:
Much stronger and deeper upper level system approaches the region Sunday and Monday and this system will certainly bring impacts if the current model projections hold. Old surface front will move northward as a warm front on Sunday and with lift increasing, showers and thunderstorms will once again erupt along and north of this boundary. Severe weather will be possible Sunday afternoon with increasing instability and shear values.

Main upper level system moves across the area late Sunday into Monday with numerous thunderstorms expected. Threat may transition from severe weather to heavy rainfall and flash flooding especially given the increasing saturated grounds after severe rounds of thunderstorms. Latest model guidance really pegs the area Sunday night into Monday morning with heavy rainfall and several flash flood factors appear favorable during this period including a good feed of moisture off the Gulf, a slow moving boundary, and exceptionally high moisture content of the air mass (PWS nearing 1.7 inches). Will also support a severe threat with a favorable splitting jet stream structure aloft and cooler mid level temperatures advecting over the warm surface air mass. Main threats appear to be large hail and wind damage, but tornadoes may also be possible.

[srainhoutx]

The overnight guidance continues to advertise a very active pattern as the first upper trough swings E into the Great Lakes Region and pushes a slow moving Pacific front across Texas into Louisiana tonight before stalling near or just S of the Hill Country. Multiple upper air disturbances are expected to ride east across Mexico as the next upper low drops further south into the Baja Region and slowly progresses E across Mexico into Texas early next week. The medium range guidance suggests this secondary upper low may move a bit slower than previously expecting setting the stage for a potential very heavy rainfall event that may extend into next Tuesday into Wednesday as the upper trough takes on a bit of a negative tilt across the Southern Plains as the stalled frontal boundary begins to drift back N. The 7 Day quantitative precipitation forecast (QPF) raises an eyebrow suggesting some locations across SE Texas into Louisiana may see rainfall totals nearing 7 inches. Very high PW values near or above 2 standard deviations above normal for this time of year with embedded disturbance tracking across the Southern half of Texas into Louisiana typically spell some potential for flash flooding. I would not be surprised to see Flood Watches hoisted within the next 36 to 48 hours for some locations mainly along and S of a San Antonio/Austin/College Station/Houston/Lufkin/Lake Charles/Alexandria/Lafayette line.

[Rip76]

Yikes on that last map if true.

[Paul Robison]

Yikes on that last map if true.

Dear Rip76:

Well, maybe no "yikes" after all. Dig this:

HGX said:

COULD BE AN ISO SVR THREAT FRIDAY NEAR AND SOUTH OF THE FRONT...BUT (remember, Rip76) THIS THREAT IS CONDITIONAL ON INSTABILITY...WHICH COULD BE LACKING. IF THE INSTABILITY IS SUFFICIENT...COULD SEE A SVR WIND GUST THREAT WITH ANY ORGANIZED CONVECTION.

Anyone have any opinions on instability with this thing? Heavy rain's all right with me, my lawn needs, but wind gust threat, well----I hope not. Hope to hear from ya'll soon. Have a super evening!

[srainhoutx]

Good morning from South Padre Island. The pre frontal trough is currently draped across Montgomery/Walker Counties extending WSW into the San Antonio area. The Pacific front with its drier air has slowed across the Hill County and likely will stall later this morning. The main upper energy that developed a deadly tornado yesterday afternoon SW and W of Chicago is moving into Canada at this time. A secondary upper low is spinning out in the Eastern Pacific slowly moving E and will be the main driver of our unsettled weather throughout the weekend into most of the upcoming work week. There is a complex of storms currently near and W of San Antonio and the weekend will likely bring several rounds of showers and storms as embedded disturbance move ENE across Mexico into Texas. While it will not be raining all the time, this stagnant pattern looks to remain in place for at least the next 5 to 6 day until that system out in the Pacific moves E. The frontal boundary to our N should begin to retreat N tomorrow allowing warm and muggy conditions to continue. The best guess is that it may take until next Thursday for a stronger front to sweep across Texas and clear this pattern...if then.

[BlueJay]

We are getting a very nice Spring shower at the moment. Up to 0.13 inches already.

[BlueJay]

So far today we have gotten 0.21 inches of rain but to me the real news is the cool temperature! Currently we are a chilly 65F. (Not quite "dog breath" enough for me)

[mckinne63]

Have had some drizzles here in Stafford, but no downpours. Looking at the current radar, looks like we may have some heavier rain headed this way. Skies are getting dark and I can see the wind starting to pick up.
Oh yes, the cooler temps are most welcome! It's currently 70 here in stafford.

[mckinne63]

Heavy rain for about an hour here in Stafford. Even heard a few rumbles of thunder. Not sure how much we got, but pool was really low, I was going to have to put water in, it is now full!

[BlueJay]

It's not really pool weather in my mind. Down to 60F now! Brrr!

[mckinne63]

No swimming yet Bluejay! Currently 63 here in Stafford.