Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/10/18

Area Forecast Discussion
National Weather Service Charleston SC
1034 PM EST Fri Feb 9 2018 .SYNOPSIS... A warm front will lift across the region tonight. This weekend, a cold front will slowly approach southeast Georgia and South Carolina from the northwest, moving and stalling near the coast late Monday night into Tuesday. Weak high pressure expected to build over the region by mid week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... Rains were tapering off across the Charleston Tri-county area as the 925 MB warm front presses northward. Warm and moist air in the boundary layer will stream atop the slightly cooler and saturated near-surface air mass and this was already resulting in widespread expansion of stratus clouds which should lower overnight. The stratus build-down looks most promising for potential dense fog over inland and southern zones, where low level winds are forecast to be lightest. The RAP13 and the HRRR both suggest dense fog will be fairly widespread by morning while the SREF favors south GA. We adjust temps and dew points higher on the evening update and maintained some 20/30 POPs overnight northern zones and reduced POPS somewhat to the south of I-16 in GA. Dense fog advisories are possible overnight and this includes the beaches and barrier islands where sea fog is expected to develop along the land/sea interface. $$ .SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/... On Saturday, the forecast area will remain between large high pressure over the Atlantic as a cold front remains west of the Appalachians. The south winds should bring upper 50s to low 60s dewpoints north across the shelf waters, supporting areas of sea fog and patchy fog across the beaches and coastal areas. South return flow is forecast to gradually strengthen across the CWA, providing weak WAA. Forecast soundings indicate a building H85 inversion through Saturday. I will keep SCHC PoPs across the far inland GA and SC counties, keeping most of the CWA dry. High temperatures are forecast to range in the low to mid 70s. Sunday, the overall pattern changes little from Saturday. However, deeper moisture should build over the forecast area as the cold front reaches the southern Appalachians late Sunday. Forecast soundings indicate that the inversion will lower to H95, with greater elevated instability. Short range guidance shows showers and a few storms developing across southern AL/GA during the morning, lifting NE across the CWA during the afternoon hours. I will forecast increasing PoPs through Sunday morning and afternoon, ranging from likely inland to CHC over the near shore waters, with a SCHC for thunder. High temperatures are expected to warm around three degrees from Saturday. Sunday night into Monday, the cold front will slow drift east across the Southeast, slowed by nearly parallel flow at H7 to H5. Pre frontal convection will gradually increase as the front approaches the region, highlighted with categorical PoPs inland to likely values east. I will include a mention of thunder during the daylight hours. The CWA will remain on the warm side of the front through the day, with highs ranging in the low to mid 70s. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Models are in decent agreement on the synoptic pattern through the long term period. Surface high pressure will wedge down the eastern seaboard Tuesday as a cold front becomes stationary either offshore or across our southern zones. Precip chances will remain in the forecast given proximity to the front. The surface high will eventually expand over the region midweek and persist through at least Thursday. Temperatures will continue to be above climo. && .AVIATION /04Z SATURDAY THROUGH WEDNESDAY/... KCHS: steady rains and occasional MVFR cigs this evening with rains diminishing toward 03Z to 04Z. Low clouds and fog should begin to develop in the wake of the rains overnight. KSAV: MVFR/IFR cigs should trend more toward IFR/LIFR overnight as stratus decks tend to expand and build down. A warm front will lift north this evening and overnight while surface moisture significantly ramps up. Only slow improvement expected late Saturday morning at both with visibility improving though ceilings will likely remain MVFR for much of the day. Extended Aviation Outlook: Flight restrictions likely in fog and/or stratus each night through early next week. Flight restrictions also possible in showers/thunderstorms late weekend through Tuesday. && .MARINE... Winds/seas have remained somewhat elevated along the SC coast as pinching gradients have been slow to relax. We adjusted some 3 hour wind speed trends with onshore flow in this region. The flow will gradually diminish overnight as the coastal warm front lifts north. Seas will remain in the 3-4 ft range near shore and 5 ft beyond 20 NM but slowly begin to subside late as the flow decreases. Reports from the Charleston pilot boat reported low cigs and vsbys down to 2 NM at times while the Savannah pilot boat reported near zero vsbys outside the river entrance. We just issued a Dense Fog Advisory for the near shore GA waters into the southern SC waters. Sea fog will likely expand north overnight as 60F dewpoints move over the low/mid 50s nearshore water temps and low-level winds decrease considerably. Saturday through Wednesday: The sfc pattern will remain between Atlantic high pressure and a slow moving cold front to the west. This pattern will support steady south winds, generally ranging between 10-15 kts. Wave heights are forecast to range from 2-4 feet within 20 NM to around 5 feet beyond 20 NM. Marine thunderstorms are possible on Sunday. The cold front is forecast to move through early Tuesday although will linger nearby through the day. High pressure will expand over the region on Wednesday. Sea Fog: A warm and very humid air mass will overspread the cooler shelf waters over the weekend. This will lead to a risk of sea fog Saturday through early next week. && .EQUIPMENT... The KCLX radar remains out of service until further notice due to major equipment failure. Repairs are ongoing. Adjacent radars include: KLTX, KCAE, KJGX and KVAX. The Downtown Charleston observation site (CHLS1/KCXM) is having occasional data issues. Use data with caution. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...Dense Fog Advisory until 2 PM EST Saturday for AMZ352-354. && $$ NEAR TERM... SHORT TERM... LONG TERM... AVIATION... MARINE... EQUIPMENT...
Area Forecast Discussion
National Weather Service Des Moines IA
535 PM CST Fri Feb 9 2018 .SHORT TERM.../Tonight through Saturday/ Issued at 304 PM CST Fri Feb 9 2018 Next round of snow expected for mainly southern Iowa tonight. Forcing ahead of the next shortwave to impact Iowa will increase and shift across the state from mid to late evening through about 12Z in the southeast. The strongest forcing will be in a fairly narrow band across southern Iowa...likely across the highway 34 corridor but strong mid-level forcing will exist all the way to the I-80 corridor. High-res models were initially pegging the highway 34 corridor but through the day were gradually shifting north and coming more in line with the NAM. I still believe the NAM is too far north bringing the higher qpf a little north of the I-80 corridor and given that the qpf for the GFS, RAP and the HRRR was about a tenth of an inch less overall...some tweaks/blends were made to the qpf in both amount and location taking the other models into consideration. Snowfall amounts will be somewhat tricky since this strong forcing is mainly mid level but the moisture is deeper and the forcing does tap into it and it is within the better dendritic growth zone of -10 to -20 degrees C. Putting it all together gives us an expected snowfall of around 3 inches near the I-80 corridor with 4 inches or so around the highway 34 corridor. A winter weather advisory will be issued for this area to coincide with when the better forcing moves in. By the 12-15Z timeframe the forcing is exiting to the east and while some light snow may continue towards mid morning Saturday, the bulk of the accumulating snow for our forecast area should be done just after 12Z. The remainder of Saturday should be dry ahead of the next system to impact the state but clouds will remain over the state and it will cold. .LONG TERM.../Saturday night through Friday/ Issued at 304 PM CST Fri Feb 9 2018 The next and last in a series of systems to affect the state will arrive on Saturday night. Surface features will be well south of the state with almost all forcing residing in the mid levels associated with the passing shortwave. The increased forcing will quickly saturate the atmosphere during the evening with snow spreading northward to around the Highway 92 corridor by midnight. The snow area will extend a bit farther north across the eastern CWA reaching the I80 corridor near Grinnell. With the forcing persisting overnight, anticipate light snow to continue until shortly after daybreak in the far southeast before subsidence and drier air arrive. With the snow ending Sunday morning in the southeast, quiet weather is expected the remainder of the day across central Iowa albeit rather cold with a canadian airmass in place along with extensive snow cover. Much of the upcoming week will see quiet weather as system drops down the west coast and becomes cutoff. There will be some moderation by midweek as the upper flow flattens somewhat across the CONUS, however this reprieve from the colder weather appears short lived as additional polar will be poised to arrive by the end of the next work week. && .AVIATION.../For the 00Z TAFS through 00Z Saturday evening/ Issued at 532 PM CST Fri Feb 9 2018 Area of snow and MVFR cigs area expected to impact southern IA including the KDSM/KOTM areas overnight. Visibilities may drop to IFR or below at times. The snow will end late tonight into Saturday morning and conditions will return to VFR. Little to no impact at other sites with VFR conditions expected to persist. Northerly winds at less than 12kts will continue through Saturday. && .DMX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 9 PM this evening to 7 AM CST Saturday for IAZ057>062-070>075-081>086-092>097. && $$ SHORT TERM...FAB LONG TERM...Cogil AVIATION...Donavon
Area Forecast Discussion
National Weather Service Lincoln IL
922 PM CST Fri Feb 9 2018 .UPDATE... Issued at 900 PM CST Fri Feb 9 2018 Expired Winter Weather Advisory across far northern portion of the forecast area a little early as persistent snow band weakened and shifted off to the east. A weak disturbance in the broad troffing across the lower 48 states is tracking east-northeast toward the Midwest from the central Plains. This disturbance has resulted in an area of light snow across Iowa, and this should impact far northern portion of forecast area after midnight, although accumulations are not expected to be significant. Otherwise, persistent/weak isentropic upglide remains over the entire area, with spotty weak returns evident on area radars. Away from the main approaching disturbance, any precipitation is likely to be freezing drizzle/drizzle or possibly flurries due to a relatively low supply of ice crystals. Do not expect much icing with any freezing drizzle that occurs. Some of the high-resolution guidance suggests light snow will be a little more widespread across central Illinois, but sounding profiles are not supportive of much snow away from the approaching disturbance. && .SHORT TERM...(This evening through Saturday) ISSUED AT 330 PM CST Fri Feb 9 2018 Extended the winter weather advisory through 9 pm for Knox, Stark and Marshall counties, and added Peoria and Woodford counties to the advisory. Additional snowfall amounts of 2 to 3 inches possible through 9 pm in these counties, with storm totals of 3-6 inches along and north of a Galesburg to Lacon line. A special weather statement will also be issued for areas from I-72 south for the light freezing rain/glaze possible from overnight into Sunday morning with the most widespread freezing rain occurring Sat night into early Sunday morning with one to two tenth inch of ice possible in southeast IL. The 21Z/3 pm surface map shows a cold front pressing southeast of a Danville to Shelbyville line. Mild temps of 50-55F ahead of this cold front in southeast IL, while much colder temps of 20-25F nw of the IL river. Colder air ushered into central and nw IL on northerly winds ahead of 1037 mb arctic high pressure over MT and ridging over the northern plains. The freezing line extended from Jacksonville to Lincoln to Gibson City. The cold front will push through southeast IL through mid evening. An 850 mb frontogenetic forced band of snow was sinking slowly southward over Knox, Stark and Marshall counties past few hours and vsbys below 1 miles at times in heavier snow band. Latest CAM models like the HRRR and RAP show this snow band lingering over the advisory area until 03Z/9 pm before it weakens and departs to the east. More snow showers to spread east from the central plains into central IL by overnight into Sat morning. Could also see patchy light freezing rain/drizzle south of I-72 overnight into Sat morning as well. Lows tonight range from 12F at Galesburg to 32F at Lawrenceville. A bit of a lull in precipitation chances later Saturday morning and Sat afternoon with pops just ranging from 20-30% then. Continued patchy freezing light rain/drizzle from I-72 south with light snow chances north of I-72. Areas south of I-70 to get warm enough for just light rain chances late Sat morning into early Sat evening. Highs Sat range from around 20F nw of the IL river, to the mid 30s Southeast of I-70. .LONG TERM...(Saturday night through Friday) ISSUED AT 330 PM CST Fri Feb 9 2018 The cold front will stall out this weekend southeast of the Ohio river over the TN and eastern Ohio river valley as a couple weak surface low pressure system track ne along it. This will like spread mixed precipitation across central and southeast IL Sat night and Sunday morning and diminish Sunday afternoon. Freezing rain appears to get as far north as I-72 Sat night and confined to southeast IL Sunday morning, with light snow chances north of there. Between one and two tenth inch ice possible in southeast IL with a light glaze as far north as I-72. Between 1-3 inches of snow possible north of I-72. Another winter wx advisory may be needed during that time frame especially for areas south of I-72. Cold highs Sunday in the lower 20s northern CWA and around 30F in southeast IL. Skies clear from the nw during Sunday night and nw winds diminish giving us a very cold night. Lows Sunday night range from zero to 5 below northern CWA over deeper snow cover, and mid teens in southeast IL southeast of I-70. Dry weather finally returns to area from Sunday night through Wed morning as 1041 mb Canadian high pressure settles se into the Great Lakes by Monday. Below normal temps continue Monday despite ample sunshine, with highs ranging from mid 20s northern CWA to mid 30s in southeast IL. Lows Mon night around 10F northern CWA to lower 20s in southeast IL. Semi-zonal upper level flow for middle of next week and developing sw winds on Tue to bring in milder temps for mid week. Highs Tue range from low to mid 30s northern CWA to mid 40s in southeast IL. Even milder on Wed with highs 40-45F northern CWA and lower 50s in southeast IL. Have slight chance of light rain showers in southeast IL Wed afternoon. Stuck close to consensus of models for forecast during 2nd half of next week, which has chances of rain showers Wed night through Fri. Rain chances possibly mixed with snow or turning to all snow chances over central IL Thu night into Fri morning as cooler air arrives behind a cold front pushing toward the Ohio river by sunset Thu. Highs Thu range from lower 40s by Galesburg to mid 50s by Lawrenceville. Highs Fri range from mid 30s northern CWA to mid 40s south of I-70. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 558 PM CST Fri Feb 9 2018 Predominantly MVFR condtions expected across the central Illinois terminals through the 00Z TAF valid time, although local IFR condtions are possible from time to time tonight. Have generally not included precipitation mention, due to expected low coverage and low confidence in exact timing/location. However, some light snow and/or patchy freezing drizzle is possible. Northerly winds will persist through the period. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...Bak SHORT TERM...07 LONG TERM...07 AVIATION...Bak
...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Saturday) Issued at 259 PM CST Fri Feb 9 2018 20Z water vapor imagery shows broad cyclonic flow over North America with a sheared out shortwave or two over the northern Rockies. This pattern leaves somewhat zonal flow over the central plains. Meanwhile a Canadian high pressure system at the surface continues to move south. The cold front has pushed through and stretches from northwest OK into western MO. For tonight the main concern is the potential for some freezing drizzle to develop this evening. All of the guidance is showing a warm air advection pattern developing over the surface high with some isentropic upglide developing over east central KS. However this lift does not persist for very long as the NAM and RAP progs show the upglide below 800mb going away shortly after midnight. Additionally forecast soundings show the better vertical motion from the isentropic lift occurring within the top or just above the saturated level while maintaining some dry air near the surface. Another complicating factor is much of the stratus over east central KS has scattered out. So the models continue to show some potential for freezing drizzle but there are also signals working against drizzle. Have a slight chance for some freezing drizzle over east central KS with no real accumulations. Considered a winter weather advisory for travel concerns, but with marginal confidence in drizzle developing will opt to hold off and let the evening shift monitor trends. Another thing to watch out for is the chance for some light snow across the far northern counties. There has been light snow moving across central NEB much of the day where the mid level frontogenesis has set up. Models show the frontogenesis moving south through the night but keep the mid level saturation just north of the state line. Therefore think any accumulating snowfall is more likely to remain north of the forecast area. Nevertheless have some chance POPs overnight for the possibility of snow. Lows tonight should not drop off to much as models keep good mixing of the boundary layer with mostly cloudy skies likely to persist. So have stayed pretty close to the prev forecast of lows from around 8 north to the middle teens south. By Saturday morning, the warm air advection pattern is progged to be gone with cold air advection and isentropic downglide over the entire forecast area. So any freezing drizzle chances are expected to be to the south and east of the forecast area. Mainly dry conditions are likely through the morning. By the late afternoon, shortwave energy is expected to dig into the central Rockies while mid level frontogenesis slides south across the state. There is reasonable agreement among the models that some mid level moisture will be on the increase as the forcing starts to come together. Therefore snow chances are forecast to be on the increase from west to east through the afternoon. Forecast soundings support the idea of all snow as cold air advection persists through the day. Highs are unlikely to warm much because of this and think they will range from the middle teens north to the middle 20s south. .LONG TERM...(Saturday night through Friday) Issued at 259 PM CST Fri Feb 9 2018 On Saturday evening an upper-level trough axis will extend from south central Canada towards the central Rockies. The cyclonic upper- level jet will be positioned over the Great Lakes region and provide divergence within the right entrance region over eastern KS. That trough axis progresses eastward Saturday night and Sunday morning. Ahead of the trough marginal positive vorticity and potential vorticity advection should add to the large scale lift over northeast KS. As a result an area of snow should spread across northern KS during the evening and gradually shift southward across the entire forecast area by Sunday morning. It appears the lift resides relatively longer over northern KS resulting in the higher QPF values. A east to west orientated mid-level frontogenetical band centered around 700 mb could also transverse across the area, which may provide additional lift to possibly enhance snowfall rates. As of now the models are in fairly good agreement with a nearly saturated profile prior to the lift arriving. An examination of cross sections reveal that the frontogenesis is initially relatively shallow in depth, flat, and partially decoupled until the trough axis approaches from the west Sunday morning. There are also hints of decrease EPV above these levels that could contribute to some banding within the larger area of snow. The dendritic growth zone is the deepest over northern KS late Saturday evening, but not much over 100 mb which is supported by SREF probabilities and model soundings. This along with cooler temperatures within the column should support snow to liquid ratios around 15:1 with closer to 12:1 in east central KS where the DGZ is shallower and the profile is slightly warmer. Given QPF generally around 0.05 to 0.20" the total snow amounts range from 1 to 3" with the higher totals north of I-70. Snow should come to an end as the trough axis swings overhead late Sunday morning. Another decent shortwave trough tracks southward over the northern Rockies early next week, which keeps the area in zonal flow aloft. This will allow temperatures to gradually warm with highs in the 50s by Wednesday. The models disagree with how that shortwave evolves over the southwestern US and when it ejects out over the plains sometime late next week. This is fairly typical with cut off low pressures in this region. There is agreement though that the system weakens into more of an open wave as it lifts northeastward. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 531 PM CST Fri Feb 9 2018 For the 00z TAFs, MVFR cigs were beginning to stream over the TAF sites, with short-range model guidance showing these cigs persisting through much of the overnight hours into Saturday morning. There is some model uncertainty with regards to when these MVFR cigs will begin to scatter out, so times may need to be adjusted in future TAF amendments. Winds will remain out of the north, with the potential for snow beginning to increase by the end of the TAF period (primarily near KMHK). && .TOP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...Wolters LONG TERM...Sanders AVIATION...Hennecke