Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/21/21

Area Forecast Discussion
National Weather Service Lincoln IL
730 PM CDT Mon Sep 20 2021 .SYNOPSIS... Issued at 715 PM CDT Mon Sep 20 2021 Thunderstorms along a cold front will bring rain to the majority of central Illinois from tonight into early Tuesday morning. Some of the storms may be strong, with damaging winds being the primary threat. By sunrise Tuesday, the line of storms is expected to be in eastern Illinois where showers may linger through much of the day. && .UPDATE... Issued at 730 PM CDT Mon Sep 20 2021 Broken line of thunderstorms stretches from west central Wisconsin to south of Kansas City early this evening. Shear values this far east are not especially impressive, but MUCAPE`s off the RAP model are above 1000 J/kg with the line as it moves into western Illinois later this evening, so some stronger storms remain a concern. Latest HRRR brings the storms in a weakening mode to near the Illinois River by 11-midnight and to I-55 around 2 am. General PoP trends in the previous forecast are on track, but made some minor adjustments over the next few hours for timing along the leading edge. && .SHORT TERM...(This evening through Tuesday) ISSUED AT 314 PM CDT Mon Sep 20 2021 Central Illinois is currently in a lull of activity ahead of tonight`s cold frontal passage. Convection is forming along the front from northwest of Kansas City through central Iowa into Minnesota. Expect this line to continue eastward through the evening and overnight hours. Short term forecasts show the greatest sfc-500 km shear in the post-frontal air mass, but sufficient shear along the front for the possibility of some severe wind gusts. In any case, most locations in central Illinois should observe a few hours of moderate to heavy rainfall in thunderstorms as the front moves through overnight. On Tuesday, expect a cooler day behind the front, with skies only gradually clearing out from west to east. Showers are expected to continue into the afternoon primarily near and east of I-57. The front has sped up a bit with this forecast, with the threat of very heavy rainfall in eastern Illinois decreasing somewhat. However, with precipitable water values of 1.5-1.8 inches in the pre-frontal air, small differences in feature movement or timing of individual cells could mean large differences in rainfall amounts. Pre-frontal storms should be capable of high rain rates. && .LONG TERM...(Tuesday night through Monday) ISSUED AT 314 PM CDT Mon Sep 20 2021 The upper trough is expected to be nearly overhead on Wednesday morning with breezy northwest winds and temperatures in the 60s much of the day. Many model solutions close off the low and keep the center near MI/IN/OH through about Thursday evening. As such, precip chances will be slow to fade out completely, especially in eastern/northern portions of the forecast area. The next short- wave trough from the northwest may begin influencing Illinois early on Friday per the WPC cluster tool, though the forecast currently reflects a short-lived warm up Friday before cooler temperatures return on Saturday. Warming temperatures and dry conditions are expected through this coming weekend into Monday. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 602 PM CDT Mon Sep 20 2021 Short term concern will be with south winds gusting 20-25 knots this evening, but focus shifts to incoming convection ahead of a cold front. Timing of the line of storms brings it to near KPIA toward 05-06Z, but a general weakening trend is expected as it gets further east. Ceilings expected to drop below 2,000 feet as the rain gets closer, then should be down to IFR levels as a cold front pushes through central Illinois between 08-12Z. Winds will shift to the northwest and still gust to around 20 knots much of the day Tuesday. A slow improvement in ceilings is expected, with VFR conditions possible by mid afternoon near KPIA, but MVFR or lower lingering in eastern Illinois well into the afternoon. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...Geelhart SYNOPSIS...AAT/Geelhart SHORT TERM...AAT LONG TERM...AAT AVIATION...Geelhart
Area Forecast Discussion
National Weather Service Lubbock TX
609 PM CDT Mon Sep 20 2021 .AVIATION... VFR conditions will continue. However, strong northeasterly winds will persist through the TAF period behind a cold front that has passed through all the terminals late this afternoon. The strongest winds are expected to be from mid-morning on Tuesday through mid-afternoon on Tuesday. && .PREV DISCUSSION... /issued 221 PM CDT Mon Sep 20 2021/ SHORT TERM... At 120 PM a cold front was along a line from Clovis to Petersburg to Paducah. The front continues exhibiting a southward movement despite the hot and well-mixed air mass that it is moving into. Have generally followed a slightly modified HRRR solution for the continued movement of the front the remainder of the afternoon and through early evening when it should be through the forecast area. An isolated thunderstorm or two is not out of the question from about 22Z to 02Z across the southeastern corner of the forecast area near where the triple point will be. The pre-frontal trough looks to have stalled as surface winds at Aspermont and locations to the east have now backed toward south. This will keep enough surface-based moisture in place to justify a slight chance mention there through early evening. Surface high pressure building in behind the front overnight will result in an increase in wind speeds with the breezy conditions continuing after sunrise Tuesday as mixing keeps higher momentum air turned over. Cold advection behind the front will bring our first day with a cooler than normal average temperature at Lubbock since August 29th. The middle of the range in MOS values shaded just a bit upward is favored for highs tomorrow given trends for much of the summer and early fall. LONG TERM... The main story for the middle of this week will be a pleasant glimpse of fall-like weather conditions as we remain under northwesterly flow aloft with slowly building upper level ridging to our west. Surface high pressure will continue to build in from the north on Tuesday evening, relaxing the surface pressure gradient and allowing winds to weaken fairly rapidly by dusk, becoming light and variable overnight. These light winds in combination with a dry post-frontal airmass and clear skies will set the stage for very efficient radiational cooling, allowing temperatures to fall into the mid 40s to low 50s across much of the area by daybreak Wednesday. A few typically cool higher elevation spots near the TX/NM border may even dip into the 30s. Wednesday will be a nearly perfect day weather-wise with temperatures near 80 and clear skies. Through the rest of the work week, temperatures will once again rise to levels slightly above normal as upper level ridging gradually builds eastward overhead. Even so, 500mb height rises will be relatively subtle, and temperatures will consequently only max out in the middle to upper 80s on the Caprock and lower 90s across the Rolling Plains by Friday. Mostly sunny skies will dominate as dry air remains firmly entrenched over the area. The upper level flow pattern will begin to evolve late week as a shortwave trough will split off from the mean flow over southwestern Canada and dive southwestward on Thursday. This troughing will eventually form into a cutoff low somewhere off the Southern California coast, which will push upper ridging eastward over Texas. This evolution will not dramatically impact our local weather aside from a slight increase in afternoon high temperatures over the weekend as upper ridging remains over West Texas. For now, there is a wide spread in guidance regarding the evolution of the upper low. There is a remote possibility depending on the eventual track and strength of the low that better moisture may be ushered back towards our area next week, resulting in cooler weather. Something to watch, but all-in-all, expect another week of dry weather locally. /DWK && .LUB WATCHES/WARNINGS/ADVISORIES... None. && $$ 01
Area Forecast Discussion
National Weather Service Marquette MI
747 PM EDT Mon Sep 20 2021 .SHORT TERM...(This evening through Tuesday) Issued at 405 PM EDT MON SEP 20 2021 A strong cold front currently analyzed form northeastern Minnesota to southwestern Iowa per MSAS analysis and surface obs will push eastward across the U.P. tonight in response to a mid-level strong short wave embedded in southwesterly flow out ahead of a long wave trough over the Northern Plains. Before that front gets here, scattered showers are expected over the next few hours over the central and eastern U.P. in response to a subtle mid-level short wave moving northward through the flow atop a moist and marginally unstable PBL. RAP shows a packet of isentropic lift on the 315 K surface (around 600-650 mb) lifting northward across the eastern U.P. over the next couple hours which will likely lead to an increase in shower coverage. Despite visible satellite showing some nucleating occurring, no lightning has been observed yet over our area. However, have maintained a slight chance of thunder for this round of showers through this evening. Tonight, that cold front will plow across the U.P. with a line of heavy showers and likely some thunderstorms, especially west half. NAM shows MLCAPE rising to around 1000 J/kg this evening ahead of the line (the GFS, as usual, shows less). There will be strong shear thanks to a 40-50 kt LLJ overhead, including 0-3 km shear vectors around 30-40 kts, but deep layer shear vectors are oriented mostly along the front. That said, there could be just enough cell growth off the front for isolated bowing segments within a larger broken line of storms tonight, hence the SPC Marginal Risk for severe weather, but with the front moving quickly eastward across the area it will probably be hard to keep any storms discrete. Models show instability waning somewhat overnight, but there should be enough to maintain at least a chance of thunder all the way into tomorrow morning when the front reaches the eastern U.P. This strong LLJ overhead will also lead to yet another night of gusty downslope winds along the Lake Superior shoreline with some 30 mph gusts possible before the front arrives and winds veer around to WNW. Tomorrow, 850 mb temps drop to around 2-3 C behind the front leading to a much cooler day. In fact, the air aloft will be cool enough that there will probably be some lake-effect clouds and rain showers over the west half. The better chance for those showers will be in the morning when there is enough remnant moisture behind the front that upslope ascent will compensate for very marginal lake-based instability. It will be breezy much of the day as well surface pressure rises around 3-5 mb/3 hr behind the front and steepening lapse rates in the CAA regime allowing some 20+ mph gusts to mix down to the surface (30 mph over the Keweenaw and along the Lake Superior shoreline east of Marquette). However, the pressure gradient weakens quickly in the afternoon leading to a decrease in wind gusts, especially after about 18z. The cool air aloft and scattered clouds will keep temps nearly steady in the upper 50s to low 60s, except in the mid 60s far south central. .LONG TERM...(Tuesday night through Monday) Issued at 340 PM EDT MON SEP 20 2021 Long term period continues to present a few opportunities for rain showers, but also a couple of very nice days. Going into the weekend, there`s still a good bit of uncertainity in the progression of a system dropping southeast through Ontario and the Great Lakes. Overall high temps through the period appear near to just above normal for a majority of the period, with a few chillier nights early in the period. Starting off on Tuesday night, continued light CAA and midlevel ridging extending across the Plains into the northern Great Lakes should help clear out skies from west to east. This should allow for raditional cooling to let much of the interior west to dip into the mid-upper 30s. Elsewhere lows should buttom out in the 40s given the delay in clearing or the moderating influnces of the lakes. Light winds in the decoupled lower atmosphere could allow for some frost formation, especially if lows exceed expectations. Ridging will continue Wednesday and given 850mb temps progged to be 1-3C, daytime highs should top out near 60 or in the low 60s. Skies are expected to be clear to partly cloudy, with some exceptions being in the downwind of Lake Superior where some light lake effect rain showers will be possible. Elsewhere on Wednesday, the earlier week trough is expected to be blocked by a building ridge off the east coast. Soon after, the trough is expected to intensify as surface cyclogensis occurrs and close off the upper level trough over the Ohio River Valley/central Appalacihans. From there, the low is progged to lift north/northeast. Models have come into fairly good agreement on this evolution, but vary some on timing and placement. Overall, rain showers associated with this system will be possible Thursday into the evening hours, mainly in the east. Upstream another shortwave is expected to dip south and reinforce the broad troughing over eastern Canada. As expected, there`s still notable differences among the guidance about whether or not another closed low will develop over the Upper Great Lakes or remain an open wave as it transits eastward. Depending on this evolution, there could be a few opportunities for rain showers this weekend. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 747 PM EDT MON SEP 20 2021 Sharp cold front and associated shra/tsra will move across the area tonight. Until fropa, expect LLWS at all terminals as 45-50kt low- level jet translates across Upper MI. With the shra/tsra at IWD/CMX, MVFR conditions will occur, followed by IFR to low MVFR as winds shift to an upslope w to nw direction. At KSAW, abundant low-level moisture and upslope flow will result in IFR cigs until fropa. MVFR cigs will then prevail at all terminals thru at least Tue morning. While IWD/CMX should improve to VFR in the aftn as cloud bases lift, KSAW may remain MVFR thru the day. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 414 PM EDT MON SEP 20 2021 Tonight, a strong cold front will pass across the lake. Out ahead of the front, southerly winds could reach gale force for a few hours over the north central and eastern lake. Issued a Gale Warning through midnight for the potential for southerly gales, but confidence is not overly high thanks to the stability with warm air over the cool lake surface. The best chance of seeing any gale force gusts will again be at the higher observing platforms. Behind the front, winds will quickly veer from south to NW late tonight. Winds behind the front are expected to be around 20-25 kts west half and 30 kts east half with some more gale force gusts possible. Could have extended the Gale Warning to cover the NW wind portion of the event as well, but decided against it since confidence in seeing gale force winds behind the front is even a bit lower than it is ahead of the front. Winds will subside below 20 kts by Tue afternoon west half, and by late Tuesday night east half, and then remain light through at least Thursday morning. On Thursday, a low is expected to lift northward out of the Ohio Valley and bend back westward towards Lake Huron. Depending on the track and strength of this low, there could end up being some gale force gusts on the far eastern lake Thursday into Thursday evening. However, confidence is still low at this point, so have decided to just mention that here rather than explicitly include it in the forecast. Westerly winds around 20 kts are expected across the lake on Friday followed by lighter winds on Saturday. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... Beach Hazards Statement until 9 PM EDT this evening for MIZ014. Lake Superior... Gale Warning until midnight EDT tonight for LSZ264-266. Lake Michigan... Gale Warning until 8 AM EDT Tuesday for LMZ248-250. Gale Warning until 4 AM EDT Tuesday for LMZ221. && $$ SHORT TERM...RJC LONG TERM...JP AVIATION...Rolfson MARINE...RJC
Area Forecast Discussion
National Weather Service San Francisco Bay Area
903 PM PDT Mon Sep 20 2021 .SYNOPSIS...The Red Flag Warning previously in effect for the North and East Bay hills and the East Bay interior valleys has been allowed to expire as winds have diminished. Tuesday looks to be even warmer than today, including areas near the water, as offshore flow continues. Cooling appears in store for Wednesday as onshore winds and the marine layer return. But that looks to be short-lived with high pressure and offshore winds returning Thursday. Dry conditions and mild to seasonably warm temperatures look to continue through the upcoming weekend. && of 9:00 PM PDT Monday...Mostly clear skies prevail districtwide along with quite mild midevening temperatures. Even around San Francisco Bay, values in the upper 60s to mid 70s are widespread. Reflecting offshore flow and the diminished solar heating of the interior as we head into autumn, not a wide range in high temperatures this afternoon away from the immediate coast. Downtown San Francisco reached 83, while Livermore was only 5 degrees warmer at 88. Tuesday looks to be warmer, and based on max temps reached today plus new 00Z model output and guidance have just made some significant upward adjustments to the forecast highs, especially areas closer to the water. Otherwise present forecasts appear on track. && of 2:09 PM PDT Monday...Red Flag Warning to continue through 8 pm this evening. Skies have cleared as offshore winds have arrived. We are seeing rapid warm-up of temperatures throughout the region as downslope winds and a drying airmass produce ideal conditions for some adiabatic warming even though 850 mb temps aren`t too warm. 2 pm temps in the mid 80s will continue to warm into the upper 80s and lower 90s through 5-6 pm before slow cooling overnight. Models do show one last burst of offshore winds across the Napa hills from 03-09z this evening but not enough coverage or strength to justify an extension of the warning. Even though winds will become light overnight there will be little or no humidity recovery thus fire weather conditions will remain near critical through the overnight hours. Smoke and haze from the Windy and KNP Complex fires is now starting to make its way south to north across the Central Coast. That smoke/haze will continue to push northward into the Bay Area by sunrise Tuesday morning. This will be impactful for air quality on Tuesday as we expect temperatures to be even hotter on Tuesday with some hazy sunshine. The pattern will support rapid warming of temps under light offshore wind flow and no marine layer. Similar to today expect temps to quickly warm into the 80s by lunchtime but then trend even hotter Tuesday afternoon with widespread temps in the upper 80s and 90s. For locations close to the coast this will be one of the hottest days so far this summer/fall. Heat risk will become moderate for sensitive populations and the smoke/haze likely wont help but the very dry airmass will allow for nighttime cooling and even getting into shade will shave several degrees off the hot temps. Even though there are no Red Flags for Tuesday conditions will continue to be near critical with the hot temps, low humidity and rapidly drying fine fuels while the long term drought continues. By late Tuesday afternoon there are signs of a southerly wind reversal coming up the coast that should bring cooling as early as Tuesday late afternoon/evening to the Santa Cruz region, then those southwest winds should push through the Golden Gate and up into the North Bay valleys overnight into Weds morning. This southerly wind reversal will occur as the main ridge weakens and a shortwave approaches far NorCal on Weds. This will lead to several degrees of cooling for Weds as onshore winds return with stratus forecast into SF Bay Weds morning. The amount of cooling for Weds should be on the order of 5-10 degrees so still warm inland but not early as hot as Tuesday. That shortwave then drops into the Great Basin by Thursday. The circulation around that low, as another ridge of high pressure builds looks to set up yet another round of offshore winds for the North and East Bay hills. The forcing for these offshore winds is slightly different and may not follow the usual diurnal trend we see of stronger winds at night. Right now expect to see increasing northeast winds across the Napa hills on Thursday overspreading the rest of the Bay Area Thursday afternoon and evening. Wind speeds look moderate but unlike the current event we should go into that offshore wind with very low humidity values that will trend as low as 10% by late Thursday afternoon with temps back into the 90s. The models had been struggling with how the low would evolve but now seem to be settling on the idea of another round of offshore winds for Thursday afternoon. Will get through this current Red Flag but have to quickly reset and see if a fresh round of Fire Wx Watches will become necessary for the Thursday event. Long range remains unseasonably warm and dry into the weekend with ridging over NorCal. && of 04:29 PM PDT Monday...For the 00z TAFs. VFR conditions through the period as the region remains under the influence of high pressure and offshore flow. W/NW winds along the coast this afternoon around 10-15 kt with N/NE winds inland. Latest HRRR smoke forecast shows increasing total smoke from wildfires to our SE beginning later this afternoon and progressing northward overnight tonight. Expect some slant range vis issues as smoke drifts northward. May also be some surface haze as well by tomorrow afternoon. Additionally, just at the end of the current taf period todays local WRF model shows a southerly wind reversal traveling up the Monterey Coast and moving into the Bay by tomorrow evening. May or may not see some low clouds into tomorrow evening, but confidence is low. Vicinity of KSFO...VFR through the period with increasing smoke aloft overnight tonight that may create some slant range vis issues. Onshore winds this afternoon around 15 kt diminishing this evening. KSFO Bridge Approach...Similar to KSFO. Monterey Bay...VFR through the period with increasing smoke aloft from nearby wildfires. The latest HRRR smoke model shows some increase in near surface smoke as well that may result in haze. As mentioned above, possible southerly surge tomorrow afternoon that may or may not bring in some low clouds into Tuesday evening. W/NW winds this afternoon 10-15 kt diminishing this evening. && of 08:03 PM PDT Monday...Light to locally moderate winds will persist through mid week. Northwest winds will then increase over the outer waters somewhat later this week. Mixed seas continue with a moderate period northwest swell and southerly swell. A longer period northwest swell will arrive mid week. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tngt...None. $$ PUBLIC FORECAST: Blier/RWW AVIATION: AS MARINE: AS Visit us at Follow us on Facebook, Twitter, and YouTube at:
Area Forecast Discussion
National Weather Service Nashville TN
800 PM CDT Mon Sep 20 2021 .UPDATE... FOR EVENING DISCUSSION. && .DISCUSSION... A couple of lingering FFW`s will likely be allowed to expire within the hour. Rainfall has dropped off considerably and the current warnings are there to account for rain that has already fallen. At this time, we are awaiting updated forecasts from the RFC to update our river products. The public forecast appears to be in good shape with POP`s diminishing as the evening progresses. The evening sounding from OHX looks much the same as 24 hours ago, with modest instability and high PWAT. Have already updated the forecast to expire the Flash Flood Watch. No further updates are planned at this time. && .AVIATION... 00Z TAF DISCUSSION. BNA/MQY/CKV/CSV...Ongoing showers across Middle Tennessee are starting to decrease in coverage. At this time, it appears that impact at our terminals during the next couple of hours will be minimal. The HRRR shows a further decrease in activity during the early evening, with an overnight lull before convection starts to increase again during the late morning and afternoon. Have included VCTS for tomorrow to handle the possibility of daytime storms. Look for MVFR ceilings to develop later tonight with some fog possible at CSV. && .OHX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ DISCUSSION......08 AVIATION........08
National Weather Service Raleigh NC
954 PM EDT Mon Sep 20 2021 .SYNOPSIS... High pressure will continue to extend across the Mid-Atlantic states through tonight. The high will drift toward the Appalachians and result in cold air damming over the western Carolinas and Virginia Tuesday and Tuesday night, as a warm/wedge front develops northeastward across the Piedmont. The front will then continue to retreat north and west across the Mid-Atlantic states Wednesday, in advance of a strong cold front that will cross the region Wednesday night. && .NEAR TERM /THROUGH TONIGHT/... As of 950 PM Monday... Surface high pressure continues to extend into the area from the northeast this evening, along with mid/upper level ridging located along/just off the Mid-Atlantic coast and into the northeast U.S. This has allowed for a continuation of dry conditions across central NC, with the moist an unstable atmosphere located just to our south and west. The is quite evident in the PW gradient across the Carolinas. The SPC meso analysis page (via the RAP initialization for 01Z) has PW`s ranging from around 0.8 inches across the north northeast Piedmont/northern Coastal Plain of central NC to around 2.3 inches across portions of the SC Lowcountry, while the 00Z/21st KGSO sounding with a PW value of 1.12 inches. Dry weather will generally continue this evening (with possibly a brief shower or sprinkles across our far southeastern counties). However, as the mid/upper level ridge begins to lift off to the northeast tonight and a deep mid/upper level trough shifting eastward across the central U.S. we will see moisture surge northward across the area, first across the western Piedmont during the early morning hours of Tuesday. The bulk of the heavy rain will remain to the west overnight as a weak impulse lifts northward in the increasing southerly mid/upper flow across the western half of NC. Low temps tonight are generally expected to range from the mid 60s to around 70 degrees. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... As of 400 PM Monday... Perturbations and anomalously rich deep-layer moisture (PWATs of 2 to 2.25") in confluent, low/mid-level flow will edge ewd and across all of cntl NC by late Tue and Tue night. At the surface, a ridge over the Mid-Atlantic will retreat wwd toward the Appalachians, while a wedge/warm front develops newd across the Piedmont of the Carolinas and VA. That front will separate probable low overcast, periods of light rain/showers, and temperatures in the lwr 70s over the wrn Piedmont from lwr/mid 80s and first half of the day dry conditions in the Coastal Plain. In those 80s along and east of that front, weak instability and CINH will support subsequent scattered to numerous showers and isolated storms during the afternoon, all of which will then continue through the night as the aforementioned moist axis drifts overhead. The GFS appears to continue to suffer from convective feedback, and to a lesser degree the NAM, with multi-inch bulls-eyes of QPF over n-cntl SC and w-cntl NC early Tue. Discounting those wet solutions and following WPC guidance, basin average rainfall amounts throughout the forecast period are expected to range from just a couple of tenths of an inch in the Coastal Plain to three quarters to one inch over the wrn/srn Piedmont, with swaths of locally higher amounts of 1-3" in briefly training convection and downpours. Lows 65 to 70. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... As of 340 PM Monday... Wednesday and Thursday: Central NC will be under the influence of southerly flow, situated between an approaching trough/cold front to the west and high pressure to the east-northeast on Wednesday. The southeasterly return flow around the high will pump moist air into the area from the Atlantic while southwesterly flow ahead of the front will advect warm moist air in from the Gulf. Aloft, the high amplitude trough extending NNE/SSW from the Great Lakes to the Deep South will move eastward toward the East Coast on Wednesday. Most model guidance has a low closing off over the mid-MS/OH Valley on Wednesday and possibly being cutoff from the parent trough over that region as the trough lifts east-northeast through eastern Canada Wednesday night. The low will drift slowly northward into the Great Lakes through Thursday, getting picked up by the next northern stream trough moving eastward through Canada Thursday night/Friday. At the surface, the cold front extending from the Great lakes, southwest through the TN Valley and into LA/TX will move eastward over/though the Appalachians late Wednesday/Wednesday night. Meanwhile, a surface low along the front over the OH Valley will quickly deepen as it lifts northward in response to the closing low aloft. The lows should become stacked over the eastern Great Lakes or Ontario by Thursday night. Uncertainty: There are still some significant discrepancies between the available models with respect to the timing of the front as it moves through NC Wednesday night/Thursday. The GFS continues to be the quickest, the EC the slowest, and the NAM in between the two. The GFS and NAM are also stronger with the high moving in behind the front. The fropa timing will of course impact rainfall, cloud cover, and temperatures through Thursday night. Precipitation: The best chances for rainfall will be on Wednesday into Wednesday night. Central NC remains in a marginal risk for excessive rainfall during that time period, but exactly how much and the duration will depend on when and how quickly the front moves through (i.e. which model pans out). PWATS should still be greater than 1.5 inches, but not quite as high as the previous 24 hours. Regardless, generally expect about an inch of rain or less, though some locally higher amounts are possible. Temperatures: Highs on Wednesday could still rise into the upper 70s to mid 80s and lows possible dropping into the mid 50s NW to mid 60s SE, but there is a medium-high bust potential on that given the above concerns. Temperatures Thursday/Thursday night should be several degrees lower, highs in the mid to upper 70s and lows in the (possibly) upper 40s NW to upper 50s east. Friday onward: The cold front should have progressed through central NC by Friday morning, with cool high pressure centered over the central Appalachians and a trough along the Carolina coast persisting through Friday night. A weak trough will move through the area on Saturday, but should be dry. Aloft, a weak shortwave traversing the base of the trough over the Appalachians will lift through the region on Friday. The parent trough will remain over the mtns as another low moves south out of central Canada and into the Great Lakes/OH valley over the weekend. Both the low and the parent trough will slowly move eastward to along the East Coast of the US through the weekend, possibly lingering into early next week. For now there is too much uncertainty to get into specifics, but generally expect this period to be dry with below to near normal temperatures. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... As of 830 PM Monday... 24-hour TAF period: VFR conditions will prevail across central NC through the early overnight hours. However, moist south/southeast flow off the Atlantic will result in ceilings lowering to MVFR and IFR by close to daybreak in the western Piedmont (including INT/GSO). A few LIFR ceilings even can`t be ruled out around daybreak, with IFR ceilings continuing through much of the day in the west thanks to cool NE flow and a CAD regime. Visibilities will also be lowering from MVFR to IFR through the day with periods of showers. At RDU and FAY, isolated showers will begin around mid- morning, increasing in coverage by the afternoon, when an isolated storm or two can`t be ruled out. This area will be east of the cool surface wedge so ceilings will only lower to MVFR in the morning and should continue mostly MVFR through the day, though some brief scattering to VFR is possible at times behind any showers. Even farther east at RWI, the dry mid-level ridge off the coast will be close enough to keep conditions VFR through much of tomorrow, with a chance for showers/storms and MVFR conditions not coming until late in the afternoon. Looking beyond 00Z Wednesday: The moist axis will continue to move eastward to include all of central NC on Tuesday night, then linger until a cold front and following much drier air sweep across the the region Wednesday night-Thursday morning. This moist axis will result in a high probability of LIFR-IFR ceilings by night and IFR-MVFR ones by day. In addition, a good chance of showers will continue through Wednesday night, with some isolated storms also possible Wednesday afternoon/evening. West-to-east clearing and a return to VFR will result behind the front on Thursday, with a continuation VFR conditions through at least Saturday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...BSD SHORT TERM...MWS LONG TERM...KC AVIATION...Danco/MWS