Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/21/18

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
705 PM CST Tue Feb 20 2018 ...Mesoscale Update... .DISCUSSION...Recent radar trends have indicated some leading stratiform from convection upstream moving into Starr and Zapata Counties this evening. In response to this, increased POPs this evening to better reflect the evolving situation. The thunderstorm potential looks conditional at the moment. SBCAPE (~2000 j/kg) and low level backed winds show some potential. The primary limiting factor is weak low level shear. HRRR has been bullish with convection across the west, however, as a capping inversion increases overnight think shear will not be the only limiting factor. If storms can maintain and move a little east into less inhibition and away from stratiform contaminated air, can`t rule out a strong storm or two...again very conditional. && 55/Frye .PREV DISCUSSION... /issued 535 PM CST Tue Feb 20 2018/ ..00z Aviation Update... DISCUSSION...Updated for latest aviation discussion below. AVIATION...The primary story this TAF cycle will be continued MVFR/IFR ceilings and brisk southerly winds. Overnight, cloud bases should remain steady or lower somewhat, perhaps as low as IFR at times for HRL. Can`t rule out some very light shower activity for HRL. As of the 00z update we are monitoring convection across northern Mexico, however, not expecting this to impact our TAF sites at this time. Southerly winds will pick back up by mid to late morning on Wednesday. Any IFR ceilings should bump to MVFR or perhaps even VFR for McAllen, especially by afternoon. PREV DISCUSSION... /issued 312 PM CST Tue Feb 20 2018/ SHORT TERM (Now through Wednesday Night): Winds have maintained their gusty character into early this afternoon, with few gusts topping 35mph but remaining shy of Wind Advisory criterion. Earlier, also had to nudge PoP`s up a bit for the remainder of the afternoon, per radar trends over the eastern counties and near- term model guidance over the west. In the larger sense, Texas remains caught in the SSW flow between the upper-level trough over the western CONUS and the strong high parked off the SE CONUS; this won`t change drastically in the short-term. This evening, GFS and HRRR are pretty bullish with scattered showers and a few thunderstorms over Zapata/Jim Hogg/Starr counties courtesy of a "ripple" in the H5 flow. NAM is a bit further north with the ripple, but have leaned away from it for the near-term. Otherwise, another warm and humid night is in store with only slight chances of showers for the remainder of the area. Temps for tonight and Wednesday were changed very little from the inherited forecast. Regarding Wednesday, flow aloft veers to more WSW and becomes a bit drier, making the column moisture a bit more diffuse. Have kept only isolated coverage PoP`s through Wednesday afternoon. Temps were teased down just a bit, but most areas will see low-mid 80s with some afternoon breezes (but down a notch from today with the PGF weakening ahead of an approaching front). Speaking of the next cold front, it will be pushing southward through Texas on Wednesday. 12Z GFS moves it into the northern/western counties between 00-03Z on Thursday and stalls it there. 12Z NAM is actually a hare slower but keeps slowly plowing it forward through the night, essentially bisecting the CWA from NE-SW by early Thursday morning. Per coordination with other Texas offices, have leaned into NAM solution for winds/temps/dewpoints starting Wednesday evening. Some uncertainty here, though. NAM pushed the last front too far south...but, this time the high pushing it is stronger (around 1040mb), though still tracks much more east than south. So, there will be a fairly tight gradient in min temps from NW to SE Thursday morning, with mid-upper 50s near APY to around 70 for BRO. Scattered showers and isolated thunderstorms are expected along and behind the front, with more isolated activity ahead of it. LONG TERM (Thursday through Tuesday): Return flow should redevelop at the coast on Thursday as a West Coast short wave trough pushes into the Southwest, supporting pressure falls over the southern High Plains, with rain chances decreasing as a remnant frontal boundary retreats north. At least that was the original thinking...per some late-breaking collaboration with other Texas offices, will lean more toward the colder NAM solution (though with some uncertainty) for Thursday/Thursday night, which will leave quite a gradient in temps across the CWA with the boundary stalled out. Front should finally lift back northward early in the day on Friday. The short wave trough will swing deep over the Southwest by Friday, with continuing southwest flow aloft over the CWA. Thus, the focus for convection will remain well to the north of the Rio Grande Valley Friday as the next cold front moves toward south Texas on Saturday. A surface cold front is forecast to push through Saturday night, but as mentioned the mid level trough will be well to the north of the area at that time, and unable to provide significant supporting upper dynamics. Elevated convection will develop across the CWA Saturday night with the front. Moderate north to northeast winds will develop on Sunday behind the front, with lingering showers. The GFS and the ECMWF differ slightly on the location/progression and strength of the front, with the ECMWF slower and weaker than the GFS on Sunday. Differences seem to decrease somewhat Sunday night, however, with high pressure settling over the area. High pressure will slide east on Monday with winds veering to east and southeast by Tuesday. Mostly cloudy skies will develop and stick around Friday and beyond, with a chance of rain on Sunday and Monday. The newer GFS run keeps temperatures lower by 5 to 10 degrees from Sunday afternoon through Tuesday, though still near to slightly above normal. MARINE (Now through Wednesday Night): Mainly moderate SE winds will persist through much of the short-term, with some backing to more easterly possible ahead of a cold front Wednesday night over the northern waters. However, persistent SE fetch across the western Gulf will keep Gulf seas elevated, especially for the waters 20-60nm out. 6-7 ft. seas will be common, with SCEC likely to continue and possibly reaching SCA criterion tomorrow night. Scattered showers and thunderstorms also expected for the northern waters Wednesday night. Thursday through Sunday night: Moderate southeast to south winds and moderate to high seas will prevail through the long term forecast as high pressure to the east dominates the Gulf. Forecast wave heights are coming in slightly higher than the short period wind driven heights one might expect for the predicted wind strength, and it is possible that some east to southeast longer period fetch component is being incorporated. Hence, periods of small craft should exercise caution to low end small craft advisory conditions will be the rule. A front will move into the area Saturday night into Sunday, shifting winds to east and then northeast. && .BRO WATCHES/WARNINGS/ADVISORIES... TX...None. GM...None. && $$ This product is also available on the web at: HTTP://WEATHER.GOV/RGV Update...55/Frye
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 && .PREV DISCUSSION... /ISSUED 546 PM CST Tue Feb 20 2018/ AVIATION [00Z TAF Issuance]... Pretty messy weather expected for the upcoming TAF period. Ceilings have improved in most areas this afternoon but will likely fall back down to IFR later this evening and overnight tonight. The models are suggesting the front and associated showers and storms may be arriving a little quicker than previously indicated. Either way, the front will push through CLL and UTS first with showers and thunderstorms before drifting into the Houston Metro (IAH, HOU, SGR, CXO) early tomorrow morning and sticking around for most of the day. Expect rounds of showers and thunderstorms throughout the day tomorrow, potentially tapering off to SHRA towards the tail end of the taf period. Ceilings may improve to MVFR or even VFR briefly before the front arrives, but should fall back down to IFR in the wake of the front. 11 PREV DISCUSSION... /ISSUED 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 MARINE... South to southeast flow will continue through Wednesday afternoon. This will keep the moisture flowing into and across the coastal waters leading to areas of fog with some dense fog possible. Have reissued the marine dense fog advisory for the 0-20 nm waters through Noon Wednesday. Improvement will be slow Wednesday morning. The persistent flow will maintain seas of 5-8 feet well offshore so will extend the SCA through 12z Wednesday. Winds relaxing as the front stalls which should allow seas to slowly subside though as the front begins to retreat back northward from the coastal areas the threat of fog returns Thursday. The warm moist flow Thursday through Saturday will likely lead to continued fog issues. Guidance in general shows a front pushing off the coast early Sunday morning probably ending the fog threat but with showers and thunderstorms. Tides will continue to run well above normal though with the lower amplitude tidal cycle don`t anticipate coastal flooding issues. 45 HYDROLOGY... In anticipation of heavy rainfall and resulting rises in rivers, tributaries and bayous, here are some items to consider when looking at hydrographs and forecasts from the WGRFC. River forecasts include 24 hours of QPF. Based on the river forecast output, no basins are expected to reach action stage. WGRFC did run contingency forecasts with 48 hours of QPF which resulted in some rises to action and minor flood stages for the Trinity, Brazos and San Jacinto Rivers. These forecasts hinge on how much rain ultimately falls upstream and is routed through the river system so there is still time to monitor conditions and forecasts for changes. Harris County bayous would need 4 inches of rainfall or more to generate flooding but this is also dependent upon rain fall rates and how quickly the rain falls. Bottom line: we will be monitoring conditions for rises on rivers and bayous but biggest impact still to be street flooding/flooding of low lying areas and poor drainage areas. KLG/SO && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 78 54 56 43 59 / 70 90 90 70 60 Houston (IAH) 79 69 74 55 75 / 50 50 90 70 60 Galveston (GLS) 75 65 72 62 73 / 20 30 70 70 50 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...NONE. GM...Dense Fog Advisory until noon CST Wednesday 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 6 AM CST Wednesday for the following zones: Matagorda Bay. Small Craft Advisory until 6 AM CST Wednesday 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. && $$ Discussion...43
Area Forecast Discussion
National Weather Service Blacksburg VA
954 PM EST Tue Feb 20 2018 .SYNOPSIS... A strong ridge of high pressure will remain off the southeast coast providing much above normal temperatures through the remainder of the week. Chances for rain increase late Wednesday into Thursday with a cold front, followed by a better chance of showers with another front by later in the weekend. && .NEAR TERM /THROUGH WEDNESDAY/... As of 940 PM EST Tuesday... Temperatures and dew points are reaching their cross-over point with fog developing within the next couple of hours, especially counties along and south of the VA/NC border. Mixing increases towards sunrise will help remove fog across the mountain valleys and foothills. The piedmont may carry fog into mid morning. Not seeing many returns upstream this evening, but models continue to carry precipitation along the southern Blue Ridge through the early morning hours. I have lowered PoPs through midnight, then raised them to 30 percent in the morning. P-type will be rain or drizzle with very little to measure. As of 620 PM EST Tuesday... Updated grids with latest observations. Minor adjustments made for breezy conditions remaining into this evening. Also made changes to dew points through the night, especially across Southside where 60F are being reported (600 PM). As of 245 PM EST Tuesday... Much of the area has finally mixed out this afternoon with residual low clouds stuck across southern sections where a weak bubble of high pressure persists. Expect these clouds to linger before again expanding back north and east after sunset when will also lose most surface mixing. However moisture will remain quite shallow into the evening so removed any pops early on to start. Moisture may deepen over far southwest sections later tonight resulting in some spotty light rain/showers/drizzle espcly NC mountains per latest HRRR but iffy given little upslope at this point. Otherwise expanse of low clouds and fog again the main issues as models show plenty of clouds east of the Blue Ridge and dense fog where skies stay clear, excluding the far west where mixing should linger. Does appear that a bit stronger southwest flow above the surface along with more clouds early may preclude widespread dense fog, but something to watch later on. Should be quite a mild overnight given rising dewpoints and warm temperatures to start most sections. Thus kept most in the 50s for lows with a few valley 40s. Weak cold front to the west will be approaching on Wednesday as the upper ridge attempts to hold tight offshore. Deepening southwest flow should enhance moisture transport into the area with forecast Pwats of better than an inch advecting in by afternoon. Forcing along the front looks quite weak given better upper support farther west closer to the actual baroclinic zone in the Midwest. Guidance does show some weak instability developing as higher dewpoints tend to coincide with heating and perhaps arrival of a weak pre-frontal type trough/outflow across the west. Appears enough ridging to hold out east to keep eastern sections dry so keeping chance pops mainly west for scattered showers with isolated coverage Blue Ridge. Cant totally rule out thunder far west but given mostly elevated instability off soundings will leave out mention for now. Could be another day of record highs with potential given a warmer start and similar warm thickness of today to see some upper 70s if more sunshine is realized out east. Otherwise bumped up highs mostly into the lower/mid 70s, while leaving areas along the southern Blue Ridge/foothills cooler per clouds and a late start due to fog. See the climate section below for details on records. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/... As of 300 PM EST Tuesday... A frontal boundary will be sandwiched between high pressure over the Great Lakes and another high just south of Bermuda. With this boundary draped over central West Virginia and northern Virginia by Wednesday night, clouds and showers will be more likely north of Route 460. Temperatures should remain considerably mild overnight with 50s and 60s expected for lows. The upper level ridge responsible for the highly anomalous warmth should begin to sag southward toward Florida on Thursday. This change should allow the aforementioned high pressure area over the Great Lakes to head eastward toward the New England States and start wedging southward along the eastern slopes of the Appalachian Mountains. As a result from the influence of northeasterly flow, the frontal boundary should begin to push southward as a backdoor cold front east of the Blue Ridge. Models still disagree on the southward progression of this cold front during Thursday afternoon through Thursday night, which adds to the uncertainty for this part of the forecast. In addition, Friday becomes more questionable due to differences in how quickly the northeasterly flow retreats once high pressure heads offshore and the frontal boundary lifts back northward as a warm front. The latest GFS and NAM solutions continue to show the backdoor cold front reaching the Virginia and North Carolina line by Thursday night and not allowing it to leave until Friday afternoon. The ECMWF, however, sends the cold front just toward Route 460, which leads to a faster erosion of the wedge on Friday and significantly warmer and drier conditions. Confidence is higher that the more significant wedge event will take place. Thus, a non-diurnal temperature trend with more clouds and showers affecting most of the Piedmont will be advertised in this update for Thursday and Friday. Friday night should stay dry as the aforementioned high pressure area south of Bermuda nudges westward toward the Mid Atlantic. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 300 PM EST Tuesday... A low pressure system will organize over the lower Mississippi River Valley on Saturday and track eastward toward the Mid Atlantic by Sunday. Model solutions continue to slow the timing of this frontal passage for our area, which appears to be during Sunday afternoon based on the GFS. Chances of rain were lowered a little on Saturday but increased a fair amount for Sunday. It is worth noting that the ECMWF solution is a little slower with the cold front than the GFS as it displays a Sunday evening frontal passage. Therefore, some questions remain on how much the moisture could linger into Sunday night and Monday morning, especially in northwest North Carolina. Eventually, high pressure should build overhead toward Monday afternoon. The upper level pattern turns more zonal by Tuesday, which looks dry with plentiful sunshine at this point. Temperatures still will reside well above normal throughout this period although it should turn a little cooler by early next week. && .AVIATION /03Z WEDNESDAY THROUGH SUNDAY/... As of 625 PM EST Tuesday... Models again show low clouds filling back in beneath the inversion overnight with low-end MVFR to LIFR across most of the region by midnight. Fog also likely again late tonight but widespread IFR vsbys iffy with a bit more pronounced southwest trajectory just above the surface layer overnight. Latest HREF has lower vsbys initially this evening before mixing out to mainly just along the southern Blue Ridge late. Therefore opted to go with more of a MVFR range in vsbys for now. The only place that should remain VFR throughout the period is KBLF although some VFR cigs likely to affect that area late tonight into Wednesday ahead of the next cold front. Low clouds will again be slow to exit eastern sections on Wednesday given only light southwest flow and deeper moisture. Also a band of pre-frontal moisture likely to affect the far western sections by midday although appears any showers should hold off until after the valid TAF period so not including mention. Otherwise plan to keep most sites under MVFR/IFR cigs Wednesday morning with most improvement in cigs near the Blue Ridge where in between trapped moisture to the east and the frontal moisture to the west. A stronger cold front looks to arrive on Sunday from the west with a better coverage of showers including continued periods of sub-VFR. Extended Aviation Discussion... May again see widespread sub-VFR develop again Wednesday night as the front approaches but stalls allowing better pooling of moisture under weak south/southeast flow. Lingering MVFR or worse conditions in showers likely Thursday with the cold front spilling south into the area. This front lifts back north Friday with continued threat of showers and potential low clouds. This front will linger nearby into Saturday with a continued threat of showers, but cigs/vsbys should a little better south of the front. && .CLIMATE... As of 330 AM EST Monday... This afternoon and Wednesday will feature well-above normal temperatures that may approach or eclipse daily record highs and daily record high minimum temperatures. It`s also possible that all- time warmest February minimum temperatures could be approached or broken in this period. Following are daily records, as well as the all-time warmest minimum temperatures recorded in the month of February, for our five climate sites with long-established periods of record: Tuesday 2/20/2018 Site MaxT Year HiMin Year BLF 67 2017 48 1994 DAN 74 1971 51 1949 LYH 76 1930 59 1939 ROA 75 1939 54 1971 RNK 69 2017 47 1991 Wednesday 2/21/2018 Site MaxT Year HiMin Year BLF 65 1996 54 1997 DAN 75 2011 55 1953 LYH 75 1930 50 1981 ROA 73 1930 48 1997 RNK 71 1986 49 1953 Warmest HiMin - February: Site HiMin Date BLF 57 Feb 5 2008 DAN 60 Feb 18 2008 LYH 59 Feb 20 1939 ROA 57 Feb 12 1932 RNK 52 Feb 16 1990 && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...JH/RCS SHORT TERM...PW LONG TERM...PW AVIATION...JH/RCS CLIMATE...AL
Area Forecast Discussion
National Weather Service Shreveport LA
915 PM CST Tue Feb 20 2018 .UPDATE... Not seeing the bowing/discrete structure in the pre-frontal storms we saw earlier this evening across portions of Northeast Texas into Southwest Arkansas with the prefrontal activity quickly decreasing in coverage and intensity. What is continuing to blossom is the convection immediately on the front and in the wake of the frontal boundary with regional radar mosaics showing convection well west of the I-45 Corridor of Central Texas. Latest 00z NAM output showing the frontal boundary, which as of 03z was oriented near a DeQueen, Arkansas, Mineola, Texas line, will continue moving very slowly south and east overnight and should be just northwest of the Shreveport/Bossier City metro area by 12z Wed. Thus, convection should continue to build and expand south and east overnight, encompassing all but our southeast half. There is good agreement in the latest HRRR and 00z NAM that our southeast zones should see very little if any precipitation overnight so have lowered pops across these zones. Otherwise kept heavy rainfall wording across the Watch area overnight with the heavier downpours likely not reaching Northwest Louisiana until near or shortly after sunrise. Updated hourly grids to mimic current conditions and to account for the frontal movement into our northwest zones but otherwise, forecast is in good shape. Update out shortly...13. && .PREV DISCUSSION... /issued 554 PM CST Tue Feb 20 2018/ AVIATION... For the 21/00z TAFs, convection is likely to affect all TAF sites this period as a strong cold front gradually move into and across the area. Flight conditions will vary initially, but IFR/LIFR ceilings and visibilities are expected at most sites, especially after 21/06z, as the convection spreads southeast across the region. The front will become stationary across the area, which should allow showers and thunderstorms to prevail at most TAF sites for much of the period. Note: Amendments are not currently scheduled for KELD because the ASOS is down, and there are no backup observation facilities. CN && .PRELIMINARY POINT TEMPS/POPS... SHV 64 66 54 67 / 90 100 100 60 MLU 67 72 57 72 / 30 100 100 80 DEQ 46 51 46 55 / 100 100 80 70 TXK 53 55 47 57 / 100 100 100 60 ELD 62 64 49 63 / 90 100 100 80 TYR 47 54 47 58 / 100 100 80 70 GGG 54 59 51 65 / 100 100 90 70 LFK 66 69 56 71 / 80 100 90 60 && .SHV WATCHES/WARNINGS/ADVISORIES... AR...Flash Flood Watch through late Wednesday night for ARZ050-051- 059>061-070>073. LA...Flash Flood Watch through late Wednesday night for LAZ001>004. OK...Flash Flood Watch through late Wednesday night for OKZ077. TX...Flash Flood Watch through late Wednesday night for TXZ096-097- 108>112-124>126-136>138-149>151. && $$ CN/13