Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/20/18

Area Forecast Discussion
National Weather Service Charleston SC
1001 PM EST Wed Dec 19 2018 .SYNOPSIS... A strong storm system will bring multiple impacts to our area tonight into Friday. High pressure is forecast to return this weekend and persist through early next week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... The current forecast is on track and only required minor adjustments. Inland high pressure will hold firm as low- level jetting begins to strengthen across the Southeast U.S. ahead a phased longwave trough extending north to south across the central states. Isentropic assent will rapidly intensity after midnight with moisture gradually working from the top down reaching near saturation for most areas by daybreak. Expect a good portion of the forecast area will be seeing rain by sunrise Thursday and pops reflect this trend with going to 90-100% by 20/12z. Lows from the upper 40s inland to the mid 50s at the beaches look on track. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/... Thursday: The mid-levels will consists of a trough axis stretching along the MS Valley in the morning. The trough will shift eastward and continue to amplify as time progresses. A weak low may develop at the base of the trough, roughly over the Southeast overnight. At the surface, a storm system will be developing to our southwest in the morning. Low pressure initially over or near the FL Panhandle in the morning will move northeastward and split into two separate lows. One will be located just to our west late at night while the other will be located/developing over the Eastern Great Lakes region. A complex series of fronts will be associated with these lows. Plenty of moisture will be across our area. Models still hint at PWATs peaking ~1.75", which is 2-3 standard deviations above normal per NAEFS. With good moisture and lift in place, POPs are at 100%. Moderate rain is expected during the daylight hours. Most locations should expect 1.5-2.0" of rain through Thursday night. Though, locally some >2" amounts are possible, especially across the Charleston Tri- County area. Precipitation will begin to taper off in the evening, with remnant showers persisting overnight. Temperatures will remain a few degrees above normal within the warm air mass. Tides: Moderate rainfall with the Thursday morning and afternoon high tides could cause drainage issues. However, the strongest onshore winds in the afternoon are expected to be with the lower of the two high tides, limiting the potential for flooding from saltwater inundation. Winds parallel the coast with the daybreak Friday high tide, so it`s still too early to determine the flood potential with that tide. Friday: The mid-levels will consist of a strong trough stretching from the Great Lakes region into the Southeast during the morning hours. The trough will move eastward with time and become negatively tilted. At the surface, the strongest portion of the storm system will be far to our northeast. However, the second low initially to our west early in the morning will quickly move to the northeast with time. Gulf Coast high pressure will begin building into the Southeast overnight. Wrap around precipitation associated with the departing low should gradually wind down during the daytime. QPF shouldn`t add up to much. Dry conditions should prevail overnight. Temperatures will be near normal. Winds: Southwest winds should be gusty in the afternoon, especially along the coast. A wind advisory may be needed, especially for the Charleston County coastline. Impacts may be more noticeable with the saturated ground. Winds will increase over Lake Moultrie Friday and could reach Lake Wind Advisory criteria with 25 knot gusts. Saturday: The mid-levels will consist of a negatively tilted trough moving off the coast, allowing zonal flow to develop over the Southeast into the afternoon. At the surface, broad high pressure initially over the northeastern Gulf of Mexico will move towards the Southeastern U.S. Dry conditions will prevail. Temperatures may be a few degrees below normal. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... Cooler and dry conditions expected to prevail this period with high pressure generally dominating. Temperatures should be near to above normal. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... VFR conditions will steadily deteriorate closer to daybreak and continue through the day as widespread rains impact the region. Expect widespread IFR vsbys and MVFR Cigs to prevail after sunrise with gusty winds impacting both terminals. Gusts in excess of 25 kts are possible. There is a potential for low- level wind shear during the afternoon, but the situation looks to marginal to include a mention for the 00z TAF cycle. Extended Aviation Outlook: A storm system will bring flight restrictions late Thursday through Friday. Gusty winds likely late Thursday through Friday night. VFR Saturday through Monday. && .MARINE... Tonight: Fairly weak winds expected this evening, then rapidly strengthening SE winds late tonight as surface low pressure moves into south central GA. Winds and seas expected to be just shy of Small Craft Advisory criteria in the GA waters around daybreak Thursday. Thursday through Monday: Both the NAM and GFS wind have increased across the Charleston County waters to justify a Gale Watch. Interestingly, the GFS shows several 50 kt wind barbs over the Georgia offshore waters closer to the Gulf Stream. Unclear if this will occur or not, but a nasty wind signature in noted in both the GFS and NAM. A storm system will bring impacts to our area Thursday into Friday, causing high winds and seas. Models indicate a short window of Gale Conditions are possible for the GA waters beyond 20 nm Thursday afternoon into evening. For simplicity with the marine headlines, we opted to only go with a Gale Watch with this zone. For all of the remaining waters within 20 nm, we have Small Craft Advisories for winds and seas starting Thursday. A second surge of winds/seas is expected Friday morning into evening for all of the coastal waters. Gale conditions seem likely, but it`s still too early to issue Gale Watches to cover this time period. Very steep wind- driven seas could peak above 10 ft beyond 10 nm and around 15 ft across the outermost portion of the outer GA waters. Additionally, the Charleston Harbor will have periods of at least Small Craft Advisory wind gusts Thursday evening into Friday. However, there is still enough uncertainty in the start time to warrant holding off on an advisory at this time. Winds and seas will trend downward Friday night into Saturday as the storm system moves away. && .HYDROLOGY... High resolution guidance is coming into better agreement that a period of heavy rain will impact mainly Southeast South Carolina Thursday afternoon through mid-evening, clearing the Charleston Tri-County area last. Both the RAP and H3R show what appears to be a nasty line of highly forced convection moving northeast across the Charleston Tri-County mid-late afternoon as high tide is peaking. Although tides are expected to remain well below advisory thresholds, heavy rains falling a few hours either side of high tide usually causes problems, especially in wet regimes such as the one the region is currently in. CPC soil mositure analysis shows soil moisture values are running roughly 600% of normal for this time of year across the quad-county area. 1-hr and 3-hr flash flood guidance values are as low as 2.2 inches in places, which could be easily overcome in pockets of heavier rainfall. A Flash Flood Watch has been issued for Charleston, Berkeley, Dorchester and Colleton Counties for Thursday from noon until 11 PM EST. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...Flash Flood Watch from Thursday afternoon through Thursday evening for SCZ043>045-049-050-052. MARINE...Small Craft Advisory from 10 AM Thursday to 1 PM EST Saturday for AMZ352. Gale Watch from Thursday afternoon through late Thursday night for AMZ350. Small Craft Advisory from 7 AM Thursday to 1 PM EST Saturday for AMZ354. Gale Watch from 7 AM EST Thursday through late Thursday night for AMZ374. && $$
Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
549 PM CST Wed Dec 19 2018 .UPDATE... Issued at 537 PM CST Wed Dec 19 2018 Updated for the 00z Aviation Discussion below. && .SHORT TERM...(This evening through Thursday) Issued at 308 PM CST Wed Dec 19 2018 Complex scenario in the short term with a wintry mix spreading in tonight. Precipitation will taper off Thursday morning from west to east, but lake effect snow will continue along the snowbelt region of northwest Wisconsin. A neutrally tilted trough will dig from the Northern Plains into the Upper Mississippi River Valley tonight. A broad low will deepen over northern Minnesota and Lake Superior. This will gradually spread precipitation in from west to east. There is still a lot of uncertainty in specific precipitation type as forecast soundings are still all over the place. At the moment it appears that a wintry mix will spread in from west to east. The heaviest precipitation is expected late tonight under better synoptic lift along the northwest side of the low. Expect more snow than a wintry mix across the Minnesota Arrowhead where up to an inch of snow accumulation is possible. Light ice accumulations are expected across much of the region, which may make slick roadways. If temperatures aloft cool quicker than currently anticipated then precipitation may change over to more snow than a mix. Flow aloft will become northwesterly and advect cold air into the region. Lows range from the mid 20s to the low 30s. The trough will slide into northern Wisconsin by Thursday evening, while the surface low weakens over Ontario. This will gradually bring precipitation an end from west to east. Expect some wintry mix as precipitation winds down as ice is lost aloft. Lake effect snow will continue across portions of the snowbelt region of northwest Wisconsin. Expect cooler highs in comparison to today due northerly cold air advection. Highs range from the mid 20s to the mid 30s. .LONG TERM...(Thursday night through Wednesday) Issued at 308 PM CST Wed Dec 19 2018 The extended period of dry weather the region has seen is likely to come to an end by next week. A few minor systems plow their way through a continued dry air mass mainly driven by short waves and residual Pacific moisture. The first arrives Saturday into Sunday with only minor snowfall accumulations. A second system may slide across on Christmas morning bringing enough snow for a white Christmas according to the GFS and ins ensembles. The Canadian also suggests this feature, but the Euro does not. Temperatures trend towards a more normal range, but still reading slightly on the high side. The main story is the potential for a system after Christmas that begins to brew finally tapping into both the Gulf and Pacific moisture sources. Models are in fair agreement for day 7 and 8, but still a lot, stressing a lot, of details to be ironed out with this. Though the first potential heavier snow maker in over a month on the horizon sure elicits some attention. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 549 PM CST Wed Dec 19 2018 A very messy forecast will continue through the evening hours across the Northland, with mainly a mix of MVFR to LIFR conditions. A mid-level trough and associated cold front will move through the region, resulting in chances of a wintry mix. Very moist low-levels, as seen in RAP and NAM model soundings, will continue for the next several hours, with a very low stratus deck and visibility reductions. The low visibilities in KDLH are expected to continue as a combination of several models indicate these low visibilities will remain through much of the overnight hours. As the cold front passes through during the overnight hours, the low stratus and vsbys will slowly scour out, but strong northwest winds will move in behind the front. Some MVFR ceilings are expected to linger despite the cold front passage. && .MARINE... Issued at 308 PM CST Wed Dec 19 2018 There is some potential for winds to ramp up Thursday morning, but only to small craft criteria. A second round of small craft winds possible Sunday. A larger system may arrive after Christmas packing gales, but still too early to tell where it will track and its intensity. && .PRELIMINARY POINT TEMPS/POPS... DLH 29 31 15 25 / 60 50 0 0 INL 24 26 8 21 / 50 10 0 0 BRD 27 30 16 28 / 30 20 0 0 HYR 31 34 20 27 / 40 50 10 0 ASX 32 35 21 28 / 50 60 20 10 && .DLH WATCHES/WARNINGS/ADVISORIES... WI...None. MN...Dense Fog Advisory until 1 AM CST Thursday for MNZ037. LS...None. && $$ UPDATE...JTS SHORT TERM...WL LONG TERM...Wolfe AVIATION...JTS MARINE...Wolfe
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
618 PM CST Wed Dec 19 2018 .SHORT TERM...(This evening through Thursday night) Issued at 230 PM CST Wed Dec 19 2018 A surface low skirts along the US-Canadian border tonight, dragging a weak cold front across the upper Midwest tonight and tomorrow. There has been quite a bit of moisture return this afternoon ahead of the front, with dewpoints rising into the upper 30s across eastern Minnesota and western Wisconsin. However, we`re still lacking in the mid-level moisture department however as evidenced by the "dry" echoes on radar this afternoon. Isentropic ascent will continue through this evening and help to saturate more of the column but it is still looking like deep moisture will be lacking by the time we see the best deformation and ascent aloft later tonight into tomorrow morning. Thus, only expecting a few hundredths of an inch of precipitation out of this system tonight through tomorrow morning. Precipitation will likely start off as drizzle later this evening, with a change over to light snow or even a light wintry mix through the overnight hours as cold air advection behind the front cools the column enough to introduce ice. With low temperatures expected to hover around freezing, and warm antecedent temperatures, widespread freezing drizzle looks unlikely to develop tonight. However, can`t rule out a few slick spots on elevated or low-lying surfaces in areas that do manage to drop below freezing. Precipitation should change completely over to snow by sunrise, with light snow looking possible during the morning commute across eastern Minnesota and western Wisconsin. Overall, little to no ice or snow accumulation is expected so impacts should remain negligible. Snow departs off to east by Thursday afternoon, with a gray and blustery day expected as brisk northwest winds behind the front gust up to 30 mph. Dry weather returns into Friday with cooler, but still above normal, temperatures behind the front. Highs will range around 30 and lows between the upper teens to low 20s. .LONG TERM...(Friday through Wednesday) Issued at 230 PM CST Wed Dec 19 2018 The longer term concerns remain chances for snow through Christmas Day and trend of potential storm system late in period. Starting out the long term, high pressure following the Thursday trough should provide some sunshine and light winds. Highs will be cooler, with lower 30s common. The next short wave trough moves along the northern and will provide a chance of light snow, mainly across the northern portion of the CWA. Moisture is meager with the trough so we expect only light snow with minor impacts. Temperatures cool a bit more into Tuesday with models diverging once again on handling the short wave trough. The GFS has more of a split flow with most of the jet energy riding across northern MN Monday night into Tuesday. It does pull a frontal boundary through the area put little in the way of QPF. The ECMWF is has shifted its energy farther south and tracks it well south of the area. If we do get any snow with this system, it will be light at best and will limit any significant travel impacts. We did retain some lower end blended PoPs for this system. The GFS sets up a nice baroclinic zone to the south of the CWA by late Tuesday. This should help intensify the developing low pressure system forecast to move out into the Colorado/Oklahoma panhandle region by Wednesday morning. The GFS has trended more southeast with the surface low track as it deepens and occludes into southern WI by Thursday morning. This would leave most of our CWA in a more favorable snow outcome. It also lifted large amounts of moisture into the region with over an inch of QPF forecast for a large swath of the CWA. The ECMWF has trended slower and a bit cooler as it did shift the low track over southeast MN. This would favor a possible mix over the southeast CWA with mainly snow again over the west and north. GEFS probability plots haven`t focused on one particular area for more significant snow/precipitation, with the GEFS plumes still showing a rather large ensemble spread. However, both deterministic models do show good potential for a higher impact type event for travel after Christmas. Travelers should continue to monitor the forecast concerning this potential storm system. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 617 PM CST Wed Dec 19 2018 Stratus that developed this morning over eastern MN/western WI has stalled out over the last couple of hours. Still, as a stronger push of west winds develops in the next couple of hours over MN, both the HRRR and LAV say this stratus deck will begin moving east, so continue to move stratus out at MSP/STC/MKT. Over northeast NoDak, the next batch of post frontal status is gathering steam as it heads this direction. The HRRR has a pretty good handle on it, so followed its timing for bringing this stratus in. By sunrise Thursday morning, this stratus will encompass the entire MPX area with 600-1200 ft cigs. We are seeing a good push of dry air at the low levels Thursday afternoon and expect a good sized clearing to develop over central MN in the afternoon that will spread south. Kept any precip out of the forecast as moisture really looks to be lacking. May see an occasional sprinkle/flurry, but nothing more than that. KMSP...The halt in the eastward progress of the clearing line is a little concerning and it is certainly possible it never gets here. One thing to watch out for is that if it does start working east again, conditions on the western edge of the stratus really deteriorate to 1sm or less vis and sub 500 ft. cigs, so we`ll have to watch for conditions to worsen before stronger NW winds arrive to help mix things out a little bit better late tonight. /OUTLOOK FOR KMSP/ Fri...VFR. Wind N at 5 kts. Sat...Chance MVFR late. Wind lgt and vrb bcmg WNW 10 kts late. Sun...Chc MVFR cigs. Wind NW 10G20 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. && $$ SHORT TERM...ETA LONG TERM...DWE AVIATION...MPG