Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 212127 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 427 PM EST Sat Jan 21 2017 .SYNOPSIS... Low pressure will track across the Carolinas tonight. A second area of low pressure over the nations mid section will intensify as it slowly tracks east across the Mid Atlantic region Sunday and Monday. The intense low will move off the New England coast Tuesday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Latest MSAS still shows the region wedged in a rather stable airmass along with lingering fog and stratus ahead of the next potent s/w approaching from the sw. Models have this moisture overspreading the region this evening then continuing to move ne through the overnight hours along the coast but tapers off to drizzle/fog across the west after 06Z. Forecast challenge is just how far north the associated warm front gets. Data suggests it gets as far north as northern NC. Best lift/support for pcpn remains over the south where categorical pops will be maintained. Mdt to locally hvy downpours will be possible for a few hours. High chc to likely pops far north. Best instability progged south of the front but data does support some elevated thunder this evening mainly across NC. Lows mid 40s north to lwr 50s south. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/... First s/w exits to the ne Sunday morning with the fa in between systems ahead of the stronger system approaching from the sw late. Plenty of low level moisture in the tsctns should result in another morning with areas of drizzle/fog and possible low vsbys. Moisture quickly returns/overspreads the fa after 18Z as strong sfc low pressure and shortwave energy aloft approach from the west. Increasing PW`s will result in moderate to locally heavy rainfall. Categorical PoPs all areas after 18Z. Warm frontal boundary progged to drift north to near the NC-VA border so kept chc thunder across southern half of fa during the afternoon with decent shear as well. SPC has SLGHT risk of severe up to the Albemarle sound with a MRGNL risk across srn VA. Appears damaging winds are the main threat. Threat will be later in the day into the evening hours. Highs in the mid-upr 50s north to mid-upr 60s south. NAM a bit faster than the GFS and much faster than the ECMWF with the movement of the stacked low, but the model trends are now more progressive than before. Deep Atlantic moisture feed results in mdt to locally downpours Sunday night tracking south to north along with thunder chcs during the evening. Categorical pops all areas with lows in the upr 40s to lwr 50s. QPF averages between 1 to 2 inches with locally higher amounts in any banded convection that may occur. Sfc triple point progged to move north of the area Monday morning with the trailing upr level low crossing the region during the afternoon. Significant dry slot progged to cut off the deep moisture feed. Main change to Mondays forecast was to lower pops to chc most areas except low end likely across the west. Tstcns also show that some BINOVC are possible leading to some instab after 18Z. Have added chc thunder Monday afternoon to account for this. Well above normal temps continue with highs ranging from the mid-upr 50s nwrn most zones to the upr 60s across the se. System continues to track ne Monday night but GFS has yet another vort lobe spoke rotating arnd the main low. Will keep low chc pops in the grids for now with this feature. Lows in the 40s. Finally get a break Tuesday as winds become NW and dry out the column. Expect skies to become pt to mstly sunny. Temps remain above normal with highs in the 50s. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... Overall, the models are in good agreement in the extended period with only a few minor differences on the timing of the frontal passage on Wed night into Thursday. But those differences are minor and the 12z GFS has moved closer to the 00z ECMWF. In the wake of the storm that will move through by Tuesday, a shortwave ridge builds in Tues night into Wednesday. This will allow for W to SW flow and should be a mild dry period. However, the upper level pattern will begin to flip with a broad trough developing over the eastern half of the country for the second half of the week. This trough will enter the region Wed night into Thursday as a sfc cold front slides into the area. This front will be lacking moisture so have limited the pops to slight chance to chance range. The best opportunity for rain looks to be in the southeastern part of the area where a little additional Atlantic moisture may be available. The timing on the front is still a little up in the air. The ECMWF moves the boundary through more quickly, while the GFS develops a wave and is slower. But the trend has been toward the ECMWF timing so focused the highest chance on Thursday. Will also need to watch the timing on the cold air arrival as well as this could impact the pcpn type, but for now don`t think the cold air will arrive until after any pcpn is gone. For Thursday night into Saturday, the region will be dominated by strong NW flow which will drop temperatures back down into the 40s for highs and lows in the upper 20s to low 30s. Have kept the fcst dry too, but will have to monitor shortwaves rotating through the upper trough as with this polar airmass, if one of these waves amplifies a bit, some snow showers would not be out of the realm of possibility. && .AVIATION /21Z SATURDAY THROUGH THURSDAY/... Widespread IFR ceilings expected to persist through the entire TAF period. with no mixing and the warm front well to south expect IFR ceilings to persist through the afternoon and overnight. A weak area of low pressure will move acrs NC and SE VA later tngt thru Sun. This will bring a decent wave of rain to spread from SW to NE across the entire region from 01z to 12Z. Also expect some LLWS in areas across SE VA and NE NC overnight. OUTLOOK...Periods of rain, moderate to heavy at times, Sunday through Monday, will be accompanied by IFR conditions. As low pressure moves off to the northeast...dry weather and a clearing sky is indicated for Tuesday and Wednesday. && .MARINE...
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Weak high pressure still is lingering over the waters this afternoon and with southerly flow aloft pushing moisture northward, seeing lots of low clouds and fog. This pattern will persist for a few more hours, before an area of low pressure move northward off the North Carolina coast. This will help to increase the winds and also with some rain showers will probably lead to visibilities increasing a little more between 1 - 3 SM. This low will track off the coast on Sunday as more showers enter the region ahead of warm front and a much stronger area of low pressure that will be moving into the Tennessee River Valley by Sunday afternoon. Expect easterly winds to increase during the day, but to remain below sca levels. The strong low will slide over the Central Appalachians Sunday night while a new areas of high pressure, centered over Eastern Canada builds down the coast. The pressure gradient will tighten off the NJ/DE coast and will extend southward into the coastal waters off the Delmarva. This will allow winds to increase to sca and possibly some gust to gale in the northern coastal zone. At this time have just raised the sca flags as the gale conditions are not a certainty and it is still about 36 hours away. The center of the low pressure system slides over the Mid- Atlantic states on Monday and the gradient relaxes so expect the winds to diminish quickly Monday afternoon. But the seas will remain up in the coastal zones for some time longer. The SCA will probably need to be extended further in time, probably into Tuesday for the coastal waters. The bay and inland waters will remain below sca conditions through the event, only getting close to sca conditions Sunday night into early Monday with winds between 15 to 17 kt. The low pressure area will slide north of the region on Tuesday and high pressure over the southeastern US will build into the area bringing a period of dry and tranquil weather to the area. The next cold front will arrive on Early Thursday. With the colder air and stronger winds slower to arrive on Friday.
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MD...None. NC...None. VA...None. MARINE...Small Craft Advisory from 1 AM to 4 PM EST Monday for ANZ652- 654-656-658. Small Craft Advisory from 7 PM Sunday to 4 PM EST Monday for ANZ650.
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&& $$ SYNOPSIS...MPR NEAR TERM...MPR SHORT TERM...MPR LONG TERM...ESS AVIATION...JAO MARINE...ESS is the U.S. government's official web portal to all federal, state and local government web resources and services.