Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/08/18

Area Forecast Discussion...Updated
National Weather Service Billings MT
859 PM MST Wed Feb 7 2018 .UPDATE... Updated forecast to increase precipitation chances over southeast Montana and lower temperatures a few degrees. RUC is delaying windshift to the southwest in Billings until after midnight so mix of freezing rain and sleet showers possible until temperatures warm towards daybreak. borsum && .SHORT TERM...valid for Thu and Fri... Active and complex weather pattern is anticipated through the beginning of the weekend. The sensible weather will revolve heavily around where the arctic boundary sets up and when it finally makes a strong push through Montana and into the mountains Thursday and Thursday night. As 3 pm the arctic boundary was located along a line from Ingomar southeast into Broadus and into western South Dakota. Precipitation was beginning to fill in to the east of this boundary as a disturbance slides in overhead. The precipitation type is going to be tricky through the next 12 to 24 hours, but generally along and just to the east of this boundary folks should be ready for all kinds of winter precipitation such as rain/freezing-rain/sleet/snow. When you get will depend how far you are to the east the the boundary edge. Currently expecting this boundary to slide west of its current position tonight. Forecasting of these arctics is difficult but it appears it will set up somewhere in a line between Harlowton/Roundup, Billings/Forsyth, Hardin/Colstrip, and Sheridan/Broadus. West of these areas folks should expect rain in any precipitation falling tonight. A mix of freezing rain/sleet/light-snow is expected for folks between and just of these cities. Finally, folks in locations like Forsyth, Baker, Miles City, and Ekalaka should expect all snow tonight. The best chance for the freezing rain will be between 9pm tonight and 9am Thursday morning before the arctic begins to make a steady push through the region on Thursday morning. Biggest changes to the forecast today involved lowering snowfall totals over much of the region (especially in western zones like Billings, Columbus, and Big Timber) as the warm downslope flow will keep a lot of the precipitation as rain initially in these areas on Thursday. However, snowfall totals will still cause quite a headache, especially east of Billings where the cold air already in place will allow the precipitation to be all snow. Still expecting at least 4 to 6 inches in Billings/Roundup and locations west while east of Billings we`re expecting at least 6 to 8 inches. The heaviest snow will fall Thursday and Thursday afternoon in locations east and north Billings/Roundup/Sheridan while locations in and west of these cities will see the heaviest snow behind the arctic front Thursday evening and early Friday morning. Much colder temperatures move in Friday afternoon with highs in the low teens and single digits. Snow will gradually end in the northeast zones near Miles City and Baker by the afternoon, but expect the snow to continue through at least Friday evening for Billings/Sheridan/Roundup and other zones west of these locations. A cold night is in store Saturday morning with nearly the entire area seeing below zero temperatures. Wind chills will drop into the negative 20s and 30s in eastern Montana Saturday morning so bundle up. Dobbs .LONG TERM...valid for Sat...Sun...Mon...Tue...Wed... Pattern will remain active in strong northwest flow aloft. The period will start with a drying trend on Saturday, but a Klondike chinook kicking in by Saturday night. Temperatures on Saturday will be chilly with fresh and deep snow cover. As winds increase Saturday night, the arctic will get driven east, allowing readings to moderate into the 30s. Temperatures may be too warm for Saturday with deep snow cover, so lowered highs a couple of degrees. Winds will increase over the western foothills Saturday night and Sunday. This could produce some blowing snow over the western foothills, especially Saturday night. Will need to watch this closely. The next system of note is set to arrive Monday and Monday night. Models are in pretty good agreement in merging an upper low from off the BC coast to an upper trough dropping southeast from the northern territories. This will drag the arctic back in and set up another snow event. The ECMWF was faster and not quite as cold with this system, compared to the GFS. The GFS was also quite a bit wetter. Have raised PoPs for this event as the GFS has been doing better compared to the ECMWF on system arrival time and intensity, of late. Northwest flow will remain through mid week with another wave arriving on Wednesday. Some indications are that the pattern will switch a bit with a trough replacing the ridge along the western coast, putting the forecast area in zonal flow. This would be for late next week and is a long way out there. TWH && .AVIATION... A wintry mix of precipitation will be over the area overnight. Expect snow E of KBIL with MVFR/IFR conditions. There will be a chance of freezing rain, freezing drizzle, sleet and snow over the KBIL area with LIFR conditions. Elsewhere, expect rain and snow showers with VFR/MVFR conditions. There will be areas of mountain obscuration with widespread obscurations over the Beartooths/Absarokas. On Thursday, good confidence that rain and snow will turn to all snow late in the afternoon through the evening as an arctic front pushes W through the area. Conditions will deteriorate to IFR/LIFR. Expect LLWS over KSHR in the morning. The mountains will be obscured. WSW surface winds in KLVM will increase in speed, with 50 kt gusts by midday Thursday. Arthur && .PRELIMINARY POINT TEMP/POPS... Thu Fri Sat Sun Mon Tue Wed ----------------------------------------------------------- BIL 026/034 901/006 906/016 007/033 014/029 007/030 016/036 37/W 86/J 42/J 00/N 24/J 31/B 01/B LVM 040/050 008/019 001/023 010/038 020/034 011/034 021/039 36/W 86/J 52/J 00/N 24/J 31/B 12/J HDN 021/028 902/008 910/013 000/031 009/027 003/027 010/035 68/J 85/J 42/J 00/U 24/J 31/B 01/B MLS 006/011 909/003 913/007 903/023 004/020 902/020 007/029 99/J 52/J 11/B 00/U 23/J 21/B 01/B 4BQ 018/031 903/007 909/010 901/029 010/027 003/025 010/034 9+/J 74/J 21/B 00/U 23/J 31/B 01/B BHK 003/008 911/003 913/008 903/023 005/022 902/021 007/031 9+/J 52/J 10/B 00/U 23/J 21/B 01/B SHR 026/041 000/008 905/015 902/033 012/030 006/029 012/036 36/W 86/J 52/J 00/U 24/J 31/B 01/B && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...Winter Storm Watch in effect from Thursday afternoon through Friday afternoon FOR ZONES 28-34-39-41. Winter Weather Advisory in effect until 11 PM MST Friday FOR ZONES 29-35-36-38-42-57-58-63. Winter Storm Warning in effect until 11 PM MST Friday FOR ZONES 30>33-37. Winter Storm Watch in effect from Thursday evening through Friday afternoon FOR ZONES 40-56-64>66. Wind Advisory in effect until 6 PM MST Thursday FOR ZONES 65-66. Winter Storm Warning in effect until 5 PM MST Friday FOR ZONES 67-68. WY...Winter Storm Warning in effect until 5 PM MST Friday FOR ZONE 98. && $$
Area Forecast Discussion
National Weather Service Columbia SC
943 PM EST Wed Feb 7 2018 .SYNOPSIS... The cold front will move through the area this evening with high pressure ridging into the area from the north Thursday. Moisture will increase again Friday ahead of a warm front. The front and associated moisture will be in the area Friday night and Saturday. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Cold front continues moving across SC and will move into the western Midlands over the next couple of hours and the remainder of the forecast area early tonight. WSR-88D returns continue showing scattered showers over much of the Midlands with the heaviest rain along the coast. Over the next several hours the remaining showers will move eastward and end with frontal passage overnight. Toward daybreak clouds will begin clearing as drier air begins moving into the region. Winds have diminished as the heaviest cells have moved east of the area so the lake wind advisory has been cancelled. Overnight lows will range from the low 40s in the northern and western Midlands to the low 50s in the southern CSRA. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Dry weather as transitional high pressure will move over the area Thursday and begin to move offshore Thursday night. Temperatures will be close to seasonal levels. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... The latest GFS shows a moisture increase Friday with an onshore flow and approaching warm front. The warm front may linger Saturday ahead of a cold front approaching from the west. The GFS shows this slow moving cold front lingering in the region into the early portions of next week, which will keep conditions unsettled into Wednesday. Temperatures will be generally close to or a few degrees normal for the majority of the longer term. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... Showers along the cold front will diminish tonight. The HRRR indicated showers will be east of the terminals by 08z. Stability has increased behind the main band of showers and wind has diminished. Also, the main low-level jet has shifted northeast of the area diminishing wind shear. Expect veering west to north wind mainly 5 to 10 knots as indicated by the GFS LAMP during the gradual frontal passage tonight. Observation trends and the GFS LAMP support mainly MVFR ceilings through much of the night. Boundary layer wind should limit fog. Drying well behind the cold front should dominate after 12z and we have forecasted VFR conditions. The GFS and NAM MOS support northeast wind 5 to 10 knots. EXTENDED AVIATION OUTLOOK...No impacts to aviation expected Thursday and Friday. Rain and associated restrictions may occur Friday night through Monday associated with a slow moving frontal system in the region. && .CAE WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. && $$ SYNOPSIS...99 NEAR TERM...99 SHORT TERM...99 LONG TERM...99 AVIATION...99
Area Forecast Discussion
National Weather Service Grand Rapids MI
933 PM EST Wed Feb 7 2018 LATEST UPDATE... Update .SYNOPSIS... Issued at 330 PM EST Wed Feb 7 2018 Lake effect snow will diminish this evening over the lake shore areas. It will remain quiet the rest of the night and through Thursday. But by Thursday night a long duration snow is expected to begin. It is expected to last 24 to 30 hours, into Friday night. The heaviest snow is expected to fall south of I-96, where 6 to 10 inches will be possible. 4 to 8 inches will be possible along the I- 96 corridor. Lighter snow is expected farther north, with 2 to 3 inches expected toward Highway 10. Stay tune for further updates on this storm. More snow will be possible Saturday night and Sunday, and again Wednesday. It will remain cold through the next 7 days with daily high temperatures in the 20s to around 30. && .UPDATE... Issued at 931 PM EST Wed Feb 7 2018 I have significantly increased POPs over our western CWA from now through 7 pm tomorrow. This is based on both radar data and the lift in the 925 to 850 layer as shown by numerous runs of the HRRR, HRRRX, RAP and NAM models. All of these models show lift in that layer west of US-131 through 7 pm Thursday. That layer is also saturated and well within the DGZ temperature range. So while the inversion heights are shallow, mostly near 5000 ft agl., we will still get snow showers. In fact our 88d snow accumulation algorithm shows 1 to 2 inches already in west central Allegan County between 5 pm and 9 pm. That area of best lift is southwest of GRR this evening but becomes solid north to south by 7 am Thursday morning from US-131 to US-31 from South Haven to Ludington. My thinking is it will snow through the night and all day Thursday in our western row of counties. Snowfall will be limited due the shallow nature of the clouds but I can see an inch two more falling in some areas by late Thursday afternoon. The Hi Res NMM does the best job of forecasting the snowfall pattern so I used that to model my pop and precipitation amounts. && .SHORT TERM...(This evening through Friday night) Issued at 330 PM EST Wed Feb 7 2018 Will allow the current lake effect headline to end. Will hoist a Winter Storm Watch for the Thursday night to Friday night period. The evening lake effect snow showers will still make for slippery travel, but it will be winding down by early to mid evening. Most areas will see an additional inch or less as surface ridging takes over by late evening. The main story will be the developing long duration storm that moves in toward midnight Thursday night. A sharpening surface boundary will develop near the MI/IN border. Isentropic upglide will increase as this boundary tightens and snow will develop north of the boundary by late evening. The snowfall will get a boost by daybreak Friday as the right entrance region of the upper jet comes overhead. Also seeing some FGEN develop in this time frame that lingers into the afternoon, especially south of I-96. The FGEN wanes by Friday evening, but upper jet doesn`t move off until late evening. Meanwhile at the surface, waves of low pressure ripples along the boundary by Friday evening. These gradually cause the boundary to sag slowly southeast. With the boundary and upper jet moving farther away, the snow should ease up into Friday evening. So all told this will be a 24 to 30 hour event with rather steady snowfall throughout and occasionally heavy bursts. The snowfall will be the heaviest south of I-96 where FGEN is most likely, along with the other forces. Areas between I-96 and Highway 10 should be in the 4 to 7 inch range, and slightly less north of Highway 10. The amount of snow south of I-96 could bring commence to halt, including closings and possible road closures. The areas between I-96 and Highway 10 will see moderate impacts, with closing also likely. One good factor to this event will be that the winds will remain light, generally 5 to 10 mph. Initially from the ESE Thursday evening, gradually turning to NNE by Friday evening. .LONG TERM...(Saturday through Wednesday) Issued at 330 PM EST Wed Feb 7 2018 The main challenge in the long term deals with the potential for impacts over the weekend. To start...a mid level trough will be approaching from the plains Saturday. As this feature nears...the moisture deepens up and the lift increases. An area of snow is expected to spread in from the west southwest during the day. The risk for snow will then persist into the night. The snow could come in more than one waves. Models are in relative agreement on this scenario. Accumulations look possible. As for impacts...they look to be light or possibly moderate as some slick roads are possible. Today we saw temperatures around 20 degrees with snow. Roads temperatures did climb into the 30s during the day. So with Saturday a few degrees higher...daytime impacts may be limited. The pattern changes once this trough goes by for early next week. The mid level flow becomes more zonal. This will act to shift the arctic airmass into Ontario and Quebec. At the surface...warm air advection develops here in the Great Lakes Region. Temperature values look to actually go near to above normal by Tuesday. Perhaps warm enough for some of the precipitation to be rain. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 652 PM EST Wed Feb 7 2018 Just about all of our TAF sites have had IFR conditions in snow showers during the past hour. As drier air moves in from the west the snow showers are expected to diminish. Normally at night the snow showers only impact the lake shore, in this case that would mean the MKG taf site. However tonight due to winds becoming more westerly, only the I-69 taf sites should remain snow free after 03z and also be VFR with ceilings. Most of the taf sites should be VFR by 18z Thursday. && .HYDROLOGY... Issued at 330 PM EST Wed Feb 7 2018 Current ice jams and potential for new ice jams to form will be the main hydrologic concern through the weekend. Cold temperatures will be favorable for new ice formation on area rivers, and will not favor the breakup of current ice jams. The next round of widespread snow is expected Thursday night and Friday, with moderate to even heavy amounts possible along and south of I-96. Water from this snow will remain locked in the snowpack and not contribute to runoff. Warmer temperatures are expected next week, with highs possibly rising above freezing Tuesday and Wednesday. A wintry mix of precipitation will also be possible Tuesday into Tuesday night. A small amount of snowmelt and liquid precipitation may create some runoff into area rivers. The combination of runoff and warmer temperatures could allow river ice to begin shifting. Flood Advisories will remain in effect for the Grand River near Portland and the Looking Glass River near Eagle until water levels fall below bankfull and stabilize. Minor flooding of low-lying areas has been reported in each location due to ice jams. Water levels in areas near ice jams will continue to fluctuate by as much as three feet until ice breaks free. Please see the latest Flood Advisory Statement for more detail. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Winter Storm Watch from Thursday evening through late Friday night for MIZ064>067-071>074. LM...None. && $$ UPDATE...WDM SYNOPSIS...JK SHORT TERM...JK LONG TERM...MJS AVIATION...WDM HYDROLOGY...HLO
Area Forecast Discussion
National Weather Service Memphis TN
922 PM CST Wed Feb 7 2018 .UPDATE...Evening Update. && .Discussion. Forecast is in good shape no significant changes. A distinct clearing line is slowly advancing across the Midsouth, oriented along a line from around Paris, TN to Tunica, MS. Clearing skies and light north winds will allow temperatures to cool into the 20s across most of the Midsouth...even the low 20s across Northern areas. Temperatures will trend warmer tomorrow and Friday with rain returning to the Midsouth late Friday. 30 .PREV DISCUSSION... /issued 238 AM CST Wed Feb 7 2018/ A cold front has just passed through Monroe County, MS. As a result, winds have turned around to the north or northwest across the entire Mid-South. Colder temperatures are filtering into the area. The freezing line currently stretches from near Harrisburg, Arkansas northeastward to Union City, TN. North and west of this line, freezing rain or freezing drizzle is occurring while south and east of this line remains rain. Latest HRRR shows precipitation quickly shifting east over the next 2-4 hours. May be allowed to cancel at least the Ice Storm Warning early. Will make a last minute call just before 4 AM. Precipitation should be completely out of the Mid-South by 18Z(12 PM CST.) Clouds will likely be slower to clear. Temperatures will remain chilly today with highs ranging from the mid 30s across the Missouri Bootheel and Northwest Tennessee to around 50 degrees near Monroe County, MS. However, highs in locations southeast of Tupelo, MS will occur at 12Z(6 AM CST). Expect temperatures to drop into the lower to mid 40s over the course of the day. Clouds will clear by tonight as SFC high pressure builds into the region. With clear skies and light winds, expect temperatures to plummet into the lower to mid 20s for lows. Temperatures will begin to rebound on Thursday as the high shifts east. Expect highs to range from the mid 40s to the mid 50s. The warming trend will continue into Friday. Although, chances for rain will begin to occur by Friday afternoon as a low pressure system begins to develop near the Texas Coast and a secondary one develops across the Southern Plains. Chances for rain will increase Friday Night into Saturday. Once the models get beyond Saturday, solutions begin to diverge on exactly how the Southern Plains low pressure system will evolve. The ECMWF evolves the system similar to the low pressure system that tracked through the Mid-South last night. Thus, changing rain over to freezing rain late Saturday Night into Sunday morning. The GFS is warmer with the system keeping precipitation rain. Meanwhile, the Canadian ends precipitation before temperatures drop below freezing. For now will keep precipitation all liquid until there is some model agreement. Models bring another system into area by Monday Night into Tuesday thus keeping rain chances in the forecast and little drying time between systems. KRM && .AVIATION... /00z TAFs/ MVFR deck will continue to influence the TAF sites early in the period...with improvement to VFR expected later tonight. North to northeast winds of 9-13kts...will diminish slightly and veer more easterly late. JAB && .AVIATION... && .MEG WATCHES/WARNINGS/ADVISORIES... AR...None. MO...None. MS...None. TN...None. && $$
Area Forecast Discussion
National Weather Service San Francisco Bay Area
340 PM PST Wed Feb 7 2018 .SYNOPSIS...A strong ridge of high pressure over the eastern Pacific will remain in place through late week resulting in dry weather conditions and temperatures well above seasonal averages. && of 01:28 PM PST Wednesday...Unseasonably warm and dry conditions prevail region- wide as a strong ridge of high pressure remains parked over the eastern Pacific. This pattern is likely to persist through at least late week with daytime temperatures a good 10 to 20 degrees above seasonal averages. Overnight conditions will remain clear with decent cooling in the valleys, yet temperatures will still be warmer than what`s typical this time of year. In the short-term, an area of stratus and fog can be see on visible satellite imagery off of the Big Sur coast as a southern surge pushes northward. The latest HRRR is the only model picking up on this and shows much of this staying offshore and not impacting the urban areas of the Monterey Peninsula through this evening. Thus, have added cloud cover and patchy fog to the forecast for the southern coastal waters. Will continue to monitor this through the afternoon and evening. The medium range models continue to show the dominate ridge weakening and retreating to the west at some point this weekend which would allow for slight cooling aloft. However, this was previously forecast to occur as early as Friday and is not trending to be later in the weekend. Thus, have kept temperatures warmer for Friday and Saturday with the cooling trend likely later in the weekend into early next week. It is at this point when the models show a mid/upper level trough dropping southward into the Pacific Northwest and then through California and the southwestern portion of the country. At this time, do not see any significant signs of precipitation across our region from this system. Thus, will maintain dry weather conditions through the forecast period. Even with the slight cooling trend expected, temperatures are likely to remain above seasonal averages into early next week. && .AVIATION...As of 3:40 PM PST Wednesday...For 00z Tafs. VFR conditions through the period expected. Southerly surge of stratus is now making its way north of the Monterey Peninsula and into the bay. Short term models as of now are not expecting much if any impact to coastal airports. Winds generally light through the period. Vicinity of KSFO...VFR. Clear skies and Light winds. As of now, no impact to KSFO is expected from the southerly surge of stratus. SFO Bridge Approach...Similar to KSFO. Monterey Bay Terminals...VFR with generally light winds. The southerly surge of stratus is currently wrapping into the bay, but mainly confining itself to the water and immediate coastal areas. There is a chance over the next few hours the stratus could reach KMRY. If that happens, not expecting cigs to go BKN although could be SCT at a few hundred feet. && .CLIMATE... Here are the record high temperatures for Wednesday, February 7, 2018 through Friday, February 9, 2018. Location Wednesday Thursday Friday SF Bay Area Healdsburg 80 in 1930 83 in 1930 79 in 1907 Santa Rosa 74 in 2006 74 in 2006 75 in 2006 Calistoga 85 in 1917 85 in 1917 79 in 2016 Kentfield 71 in 2006 74 in 2016 74 in 1945 San Rafael 74 in 2016 74 in 2016 70 in 2016 Napa 79 in 2011 78 in 2016 75 in 2006 San Francisco 73 in 2006 75 in 2016 73 in 2006 SFO Airport 73 in 1987 73 in 2016 71 in 2016 Half Moon Bay 75 in 1987 77 in 1987 77 in 2016 Oakland Airport 74 in 2016 79 in 2016 70 in 2016 Richmond 74 in 2015 78 in 2011 75 in 1988 Livermore 78 in 1917 78 in 1917 77 in 1917 Moffett Field 73 in 1987 75 in 2016 74 in 2006 San Jose 76 in 2016 78 in 2016 76 in 2016 Gilroy 76 in 2011 78 in 1963 78 in 2012 Monterey Bay Area Santa Cruz 85 in 1954 85 in 2016 78 in 2006 Salinas 82 in 1987 83 in 2016 84 in 2006 Salinas Airport 84 in 1954 83 in 1954 81 in 2016 Monterey 85 in 1954 84 in 2016 85 in 2016 King City 85 in 1954 84 in 2006 86 in 2006 && of 01:24 PM PST Wednesday...A southerly wind reversal of low clouds and fog is working northward along the Big Sur coast late this afternoon and will continue to spread towards Monterey Bay this evening. Otherwise light wind and seas will prevail through Thursday under high pressure across the coastal waters. Northwest winds will increase later Friday into Friday night as a strong pressure gradient sets up near Cape Mendocino with strong winds into the weekend. A large nw swell train may arrive by Monday after a weekend of fresh wind waves. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tday...None. $$ PUBLIC FORECAST: RGass AVIATION: AS MARINE: RWW Visit us at Follow us on Facebook, Twitter, and YouTube at:
Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
707 PM EST Wed Feb 7 2018 .UPDATE (Overnight through Thursday)... 00Z water vapor and H4 RAP analysis shows an upper level pattern consisting of broad ridging over the western half of the nation and broad troughing covering the eastern states. The Florida peninsula resides generally south of this trough on the northern periphery of Caribbean upper ridging. One shortwave trough exiting the southern MS valley around the base of the eastern CONUS trough will be shearing out as it migrates eastward overnight...but is forecast by ensemble guidance to provide the atmospheric push to propel a weak cold front down into the northern/central peninsula by Thursday morning. This front is currently located at the surface back toward the Florida peninsula and north-central Gulf of Mexico...and has been supporting widespread showers/storms along the northern Gulf coast through the day. However, as the front moves south later tonight and Thursday will drop south of the best large scale forcing for ascent...and also into a region of much shallower column moisture. With all these factors...agree with the NWP ensemble guidance which show the showers becoming much less organized by the time they reach our far northern Nature Coast zones...and likely be completely gone before the frontal forcing reaches the I-4 corridor of the state. So...current forecast does bring a few scattered showers into the Nature coast overnight/Thursday morning...but certainly not a washout (like some recent systems), and rainfall accumulations will be very light. South of I-4...doubt we will see anything in terms of shower activity from the front. Temperatures the next 24 hours will remain well above average for early February. Even behind this front...there is not much in the cooler air...and locations south of I-4...will barely notice its passage. Low temps overnight ranging from around 60 up toward the middle 60s across central and southern portions of the region. High temperatures Thursday ranging from the lower 70s behind the front up toward the middle/upper 70s through the I-4 corridor...and lower 80s further south. The greatest forecast dilemma the next 12-18 hours will be the potential development and evolution of sea-fog. I would love to say sea fog is an easily identifiable event and easy to forecast. The fact of the matter is that sea fog is extremely difficult to forecast in detail. There certainly are good indicators of sea fog potential...but everything at the surface and above the surface have to play perfectly together to develop the fog...and then have to remain in alignment to keep the fog going. Very subtle changes and differences over time can easily bust a forecast. To make matters worse...NWP is highly biased toward being aggressive with its development and many models give numerous false alarm forecast during a season. Therefore...often we have to go off knowledge of past experience and simply give this fog forecast a "best shot". Since the economic impacts to shipping are so high with any sea-fog event...especially in and around Tampa Bay...we often have to lean toward a more aggressive forecast...and doing that overnight/Thursday morning. We are not going to see any fog development until the sea- breeze circulation has completely dissolved. The sea-breeze results in a highly mixed environment and would prevent the stability needed for start the sea fog process. Therefore...we got a few more hours before the potential goes up. Once we get closer to midnight and beyond...fog potential over the coastal waters and developing onshore goes up...especially to the north of Venice/Sarasota where SSTs are coolest and the SST/dewpoint depression is greatest. One of the concerning factors later tonight is the fact that as the front starts to approach, we end up in a col region of the surface pressure gradient. Within this col region winds will be very light. Contrary to radiational land based fog...where light/calm winds are required...sea fog actually needs some air movement to form. We almost certainly have the dewpoint depressions in place across the northern half of the area...but it is very border-line whether or not we have enough air motion to actually get the fog to develop. However...for now...lets assume it does. Would anticipate low visibility moving onshore from around Sarasota...up through portions of Tampa Bay and then along the Nature Coast. These areas run the greatest risk of significant visibility issues during the Thursday morning commute. Once the sun comes up...diurnal mixing would slowly erode the sea fog back toward the coast...with a combination of mixing and frontal passage ending the threat for most location by the second half of the day. Will be closely monitoring satellite and model data through the evening and update the forecast as it relates to temporal and spatial low visibility as necessary. && .AVIATION (08/00Z through 09/00Z)... When sea fog potential is in the forecast...the forecast for terminals near the coast is always a difficult one. With sea fog being such a subtle phenomena, the range of possibilities and timing of visibility restrictions is wide. Therefore, tried not be get too detailed just yet. Will not see any sea fog at the coast until the sea-breeze has completely dissolved. Therefore...bring visibility down around midnight...with IFR conditions for the late overnight hours and first couple daylight hours of Thursday. A gradual improvement in conditions then begins with daytime heating...with any fog working back toward the coast and eventually back out over the water. Will monitor satellite and model trends through the evening and update this discussion as necessary. && .Prev Discussion... /issued 235 PM EST Wed Feb 7 2018/ SHORT TERM (Tonight-Thursday)... Deep Hudson Bay U/L vortex is creating extensive cyclonic circulation over much of North America with a L/W trough axis through the central U.S. An U/L disturbance was rotating through the base of the trough and will quickly eject and lift quickly northeast overnight. An associated area of low pressure will move rapidly from the central Appalachians through the northeast tonight, with a trailing cold front pushing into north Florida. However, U/L support will be moving away from the region which will cause shower activity along the boundary to dissipate as it sinks gradually south over north Florida...with only a slight chance of a shower over the nature coast. Low level moisture will pool ahead of the front which will aid fog development tonight across west central and southwest Florida, and fog may be locally dense. Dew points in the mid 60s will also create favorable conditions for sea fog to develop after sunset. Main inhibiting factor will be the weakening gradient over the water, which may cause mixing to become too weak for sea fog formation. The frontal boundary will stall across the central Florida peninsula on Thursday as it becomes parallel to the U/L flow. Main impact will be slightly drier air advecting across portions of the region with dew points on Thursday dropping into the mid 50s north to the lower 60s central. A strong subtropical U/L ridge was centered over the Bahamas and extended across the Gulf of Mexico and the Florida peninsula. Strong large scale subsidence associated with the ridge will allow temperatures to remain above climatic normals. LONG TERM (Thursday Night-Wednesday)... General troughiness over the country while weak upper ridge from the NE Caribbean nudges east of the state through the weekend with SW flow developing aloft bringing some energy off the Gulf through mid next week. Frontal boundary washes out over the area to start the period with high pressure north of the region moving into the W Atlantic this weekend to keep SE-S low level flow over the FL Peninsula this to end the weekend and into next week. Decent mean layer moisture and moving over the region to combine with diurnal heating, bay/sea breezes to keep isolated to scattered rain chances in the forecast. Expect a warm, muggy, and somewhat unsettled pattern as temperatures will remain above normal through the period. MARINE... Potential for sea fog developing tonight, otherwise rather benign conditions next several days with no other hazards expected. FIRE WEATHER... No fire weather hazards are expected next couple of days as the relative humidity is expected to remain above critical levels each day. && .Preliminary Point Temps/PoPs... TPA 66 78 63 79 / 10 20 20 10 FMY 67 83 65 82 / 10 20 20 20 GIF 65 80 63 81 / 10 20 10 20 SRQ 64 78 63 78 / 10 10 20 10 BKV 62 78 60 80 / 10 20 10 10 SPG 65 78 63 78 / 10 20 20 10 && .TBW WATCHES/WARNINGS/ADVISORIES... FL...None. Gulf waters...None. && $$ UPDATE/AVIATION...Mroczka Previous Discussion...Oglesby/Davis