Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/19/20

Area Forecast Discussion
National Weather Service La Crosse WI
527 PM CST Fri Dec 18 2020 .SHORT TERM...(This evening through Saturday) Issued at 245 PM CST Fri Dec 18 2020 Forecast concerns in the short term will be precipitation type, coverage, and snow amounts with the light wintry mix of precipitation that moves through tonight. Latest radar observations and metars since 12Z show a leading area of echoes aloft with some light precipitation in northeast South Dakota and also farther to the north across northern MN through late morning. Early this afternoon, the snow band has increased from Hibbing toward Alexandria with moderate snow. The 12Z MPX sounding had 0.29 inches of precipitable water yesterday at 12Z and was up to 0.40 inches this morning. A narrow moist layer around 1200ft was seen with a deep dry layer to around 11,000ft. Visible satellite imagery has some thinning and also a little convective look to some of the development over parts of southern MN, northern IA, and northeast Neb. The lowest visibilities with the snow are across northern Minnesota with 1/4 mi vsby. Frontogenesis is stronger across northern and central MN with steep lapse rates of 6.5 to 7.5 deg C. The left front exit region of the jet is increasing upper level divergence across Iowa into the rest of the forecast area by 00Z then shifts off to the east. The CAMs show and uptick in precipitation as the trough/upward motion increase this evening. This can also be seen in the 0-2km RAP rh as it fills in 23Z and beyond. The RAP forecast soundings early this evening do have ice being introduced with lift in the dendritic growth zone. Meanwhile...the surface front is pushing into western MN and eastern Nebraska. Will maintain higher pops, however light precipitation amounts. Due to the warmer surface temperatures a mix is possible, but once the stronger lift occurs have it more snow. Snow amounts mostly a trace to a half an inch. Temperatures drop from the upper 20s to the teens behind the front. This will need to be watched as we are starting above freezing. Some locations will see their Saturday high just after midnight with the colder air coming in for Saturday. .LONG TERM...(Saturday night through Friday) Issued at 245 PM CST Fri Dec 18 2020 At least a few snow chances through the extended with temperatures turning much colder for Christmas Eve/Christmas Day. The shot of cool air behind the front Saturday is short-lived with return flow already by Saturday night. Upstream, the next wind shift is pushing through the Dakotas and comes through dry Sunday. The next clipper-type system is a little bit more robust and dives southward toward the forecast area Sunday night into Monday. The GFS/EC/NAM/CMC all have a light snow signal, however our blends are dry. Did go ahead and keep the chance for light snow going. Mostly less than an inch, however some of the EPS ensembles for Medford have some higher 1 to 3 inch amounts. Ridging for Tuesday, then the active pattern continues with a Central Plains trough. The strength of the trough is in question and this can be seen with the EPS. the ensembles are showing a trace to 1 inch, however there is a large spread with a few in the 3 to 8 inch range. The very cold temperatures associated with the surge of cold air Wednesday night if combined with moisture would be easier to snow. Temperatures plunge Wednesday night and remain cold Christmas Eve/Christmas Day with sub-zero wind chills. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 526 PM CST Fri Dec 18 2020 A trough of low pressure will move through the area tonight bringing with it a mix of light rain and snow. Expecting this in the 02-06z time frame at KRST and 04-08z time frame at KLSE. Very minor accumulations of snow are expected with a trace to perhaps a 1/4. Look for vsby generally in the 5-6sm range in the precipitation, but could see some further reductions if we see a more vigorous snow shower pass through. Otherwise, deteriorating cigs expected with the precipitation with IFR lingering into Saturday morning. Gradual improvements Saturday with KRST VFR by 19z while KLSE remains in MVFR through the afternoon. Plan on light south winds this evening, swinging to the northwest in the 9-15kt range after midnight into Saturday. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ SHORT TERM...Zapotocny LONG TERM...Zapotocny AVIATION...DAS
Area Forecast Discussion
National Weather Service Charleston SC
1008 PM EST Fri Dec 18 2020 .SYNOPSIS... High pressure will prevail through Saturday. Complex low pressure will impact the region Saturday night into Monday. Then, high pressure will build into the area through mid week. A strong cold front is expected to cross affect the area Thursday, followed by colder high pressure late week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... There are a few subtle nuances in the forecast tonight, with the main concern regarding how much of the stratocumulus over the Atlantic advects onshore, and whether or not any fog/freezing fog can occur. Satellite images have shown a distinct trend toward increasing stratocumulus brushing onshore of coastal McIntosh and coast Liberty County. This is the result of a slightly more favorable onshore trajectory than further north, along with increasing isentropic ascent. As a result we have increased cloud cover those areas through the night, which will impact the diurnal temp curve. Elsewhere it`ll stay clear or mostly clear with just some wisps of thin cirrus in places. As a cold as it`ll get, we anticipate that steam fog will form over and near warmer bodies of water inland such as ponds, creeks and marshy regions. There will also be at least some ground fog, especially across Georgia. Given the sub-freezing temps this would be considered freezing fog, albeit shallow in nature. The NAM and RAP indicate that fog could become more than just ground fog, but condensation pressure deficits for the moment do not look low enough for such an occurrence. Expect a huge range of min temps, from as cold as the upper 20s northwest tier to around 40F near the coast where north- northeast breezes and/or clouds will modify the otherwise cold air mass. Previous discussion... Other than thin cirrus at times through the night, skies will remain clear as the marine-induced stratocumulus stay generally offshore. Toward morning some of them could advect onshore of McIntosh County as the weak isentropic ascent develops and the low level flow veers to the east-northeast. Strong radiational cooling is already underway and will allow for freezing temps to cover inland locations all the way to near the US-17 corridor. Coldest will be the northwest tier where upper 20s will be common. It you`re at or near the coast, min temps will average 35-40 degrees. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/... Saturday: High pressure will prevail at the surface and aloft. After a cold start, temperatures will only recover into the middle to upper 50s Saturday afternoon, a few degrees below-normal for mid- December. Also, ahead of low pressure developing upstream, high clouds will spread across the region, especially during the afternoon. Saturday night: An upper trough to the west will amplify and advance toward the east. Deepening moisture transported from the southwest, an overrunning regime supported by an inland surface wedge of high pressure/a coastal trough and increasing deep layered forcing for ascent should support increasing coverage of showers, especially after midnight. Pops later Saturday night range from around 50 percent inland to around 30 percent far south/east. Higher PoPs could eventually be required for inland/northern locales. Low temperatures should range from 40-45F across a wide swath of inland counties to 45-50F on the beaches. Sunday: The initial episode of overrunning rain/showers will advance toward the east/northeast during the morning. Morning PoPs range from around 50 percent most areas except 30-40 percent far south, and higher PoPs could eventually be required for some northern/inland areas. Then, a relative lull in precipitation coverage could develop between the morning event and another round of forcing for ascent/enhanced moisture produced by the approaching upper trough/associated surface low ejecting northeast from the Gulf of Mexico later in the day or Sunday night. However, sufficient uncertainty exists regarding the interval between these events, so differences between Sunday morning/afternoon PoPs are subtle. Otherwise, expect a mainly cloudy day with high temperatures ranging from the lower/middle 50s inland to the upper 50s/lower 60s near the coast and across southern counties. Sunday night into early Monday: A sharp mid/upper level trough and associated surface low should cross the region, producing another round of rain/showers. Elevated instability could even support a few lightning strikes/pockets of heavier rain, although the probability for thunder remains too low to mention within forecasts. Per area consensus, PoPS are capped around 50 percent, but locally greater PoPs could eventually be needed. Low temperatures 45-50F should be common. Monday: Some deterministic models push drier air across the region early, while other guidance depicts persistent moisture/showers associated with the upper low/cold pool aloft. Thus, the decrease in PoPs remains conservative for this forecast, with at least slight chance PoPs hanging on along the coast into the afternoon. The uncertainty regarding PoPs also translates the potential high temperatures. For now, forecast highs remain close to normal, in the upper 50s to lower 60s. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Surface high pressure west of the area Monday night will build eastward crossing the area Tuesday night and Wednesday before moving into the western Atlantic by Wednesday night. Models are all in agreement that a cold front will move through the area Thursday into Thursday evening with some rain chances starting Wednesday night and continuing perhaps into Friday. There is decent confidence in this part of the extended forecast. However, there is a lot of uncertainty regarding the strength of the cold front and how cold it gets behind the cold front and this will impact temperatures on Christmas Day and into the weekend. && .AVIATION /03Z SATURDAY THROUGH WEDNESDAY/... VFR through 00Z Sunday. Extended Outlook...Increasing probability for MVFR/IFR ceilings from late Saturday night through Sunday night/early Monday. VFR conditions return Monday and persist through Wednesday. && .MARINE... Overnight: High pressure will dominate with primarily N-NE flow over the waters. A lingering tight pressure gradient will make for 10-15 kt winds with occasional gusts up to 20 kt. Seas will generally range from 2-4 feet across the waters. High pressure will produce NE winds 10-15 kt and seas 2-3 ft Saturday into Saturday evening. As a coastal trough develops later Saturday night into Sunday night, wind speed should remain below 15 knots, and wind direction will vary with time and will depend on the position of the coastal trough. Then, as surface low pressure tracks NE along the Gulf Stream, a tightening surface pressure gradient will support strengthening offshore winds starting later Sunday night, and offshore winds could support Small Craft Advisory conditions in some areas, especially AMZ350 and AMZ374, Monday into Tuesday. Then, more tranquil conditions should develop for a brief period around midweek before a strong cold front advances through the region Thursday. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM... SHORT TERM...SPR LONG TERM...MTE AVIATION... MARINE...
Area Forecast Discussion
National Weather Service Lincoln IL
927 PM CST Fri Dec 18 2020 .SYNOPSIS... Issued at 247 PM CST Fri Dec 18 2020 Mild temperatures with highs into the lower to mid 40s are expected Saturday, but a cold front will bring a chance of light rain or drizzle through much of the day. The weather will be dry Sunday and temperatures will remain mild in the lower 40s for high temps. && .UPDATE... Issued at 920 PM CST Fri Dec 18 2020 Expansive cloud cover will remain across our CWA overnight, due to strong WAA southerly flow bringing increasing mid-level moisture. VIRGA will work to progressively saturate the lower levels the rest of the night. Radar returns already showing up across our southern counties are deceptive due to a dry sub-cloud air mass. Cloud heights of 6K FT are starting to develop as of 9 pm. However, we do not expect precip reaching the ground until after midnight, with better chances toward sunrise on Saturday. Have continued the start of precip in the forecast at 11z/5am, but a few sprinkles could reach the ground as early as 3 am for the I-72 corridor where the high res guidance is pointing toward saturation developing sooner there. The cold front is projected to reach our western counties between 6-9am Sat morning, then progress slowly eastward to near the I-57 corridor by 00z/6pm. Rainfall in most of our CWA will be spotty Saturday morning into early afternoon, before a more focused area of rainfall develops ahead of the front for our southeast counties Saturday afternoon. That progression is already handled well in the forecast. Only minor updates were done to the short term forecast, with minimal impact on the forecast details. && .SHORT TERM...(This evening through Saturday) ISSUED AT 247 PM CST Fri Dec 18 2020 Low pressure is centered over eastern NE this afternoon and is progged to shift across southern WI Saturday with a trailing cold front sweeping across Illinois. Meanwhile a southern stream shortwave is over the Desert Southwest this afternoon and expected to shift east across the lower Mississippi Valley Saturday. This southern wave will keep deeper moisture well south of Illinois which will result in fairly light and possibly sparse precip coverage across central Illinois with frontal passage. Forecast soundings show the column sufficiently warm for rain through the event, and while the column does cool some behind the front, loss of ice nuclei and above freezing surface temps will result in just some drizzle. Finally, there is a fairly zonal pattern aloft with little in the way of cold air behind the cold front. Temperatures will warm into the lower to mid 40s ahead of the front Saturday, and will remain seasonably mild behind the front with highs in the lower 40s Sunday. .LONG TERM...(Saturday night through Friday) ISSUED AT 247 PM CST Fri Dec 18 2020 The upper pattern will become increasingly amplified through the upcoming week with well above normal temperatures early in the week giving way to an arctic air mass late in the week. On Monday, a clipper system will bring a chance of precipitation to the northern half of Illinois. There remains some uncertainty on the exact track of this system and for now there is only a slight chance of precip along and north of I-74. Meanwhile, upper ridge will slowly build east through the first half of the week supporting above normal temperatures with highs in the mid to upper 40s while a few southern locations push into the lower 50s. A strong shortwave will move onshore over the Pacific Northwest early next week and carve out a deep trough as it moves across the mid section of the country by Wednesday. A deep surface low will develop over the northern Great Plains in response and shift east into the Upper Great Lakes Wednesday with a strong cold front pushing across Illinois. Temperatures will plunge behind the front as h85 temps of around -20C advect over the Midwest through the latter half of the week. This will translate to afternoon highs in the 20s and overnight lows in the teens and single digits. Near zero or below zero wind chill values appear possible for Christmas eve and Christmas day. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 556 PM CST Fri Dec 18 2020 South-southeast wind gusts will diminish by early this evening, but sustained winds will continue in the 10-15KT range. With the decrease in surface winds and the increase of a low level jet over the region, LLWS will become a concern to aviation. 50KT winds will develop just above the ground and continue overnight. A cold front will bring spotty rain on Saturday, mainly southeast of the terminal sites. The latest HRRR and RAP updates show a continued potential for IFR and drizzle during the day tomorrow. Therefore, we did include a trend to IFR clouds late in the 00z TAF period. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...Shimon SYNOPSIS...Deubelbeiss SHORT TERM...Deubelbeiss LONG TERM...Deubelbeiss AVIATION...Shimon