Scientific Forecaster Discussion
000 FXUS61 KGYX 231645 AAA AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 1145 AM EST Tue Jan 23 2018 .SYNOPSIS... Low pressure will move east across southern New Hampshire and coastal Maine today, spreading steadier rain across the region ahead of it. Temperatures will still be near or below freezing especially in interior sections, so some icing is expected. Temperatures will warm behind a warm front over southern New Hampshire and coastal Maine during the day today. As the low moves east this evening it will drag a cold front through the area with cooler temperatures expected for the rest of the week as high pressure builds in. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Update...Main precip shield has arrived...and some heavy precip rates are possible for the next couple of hours. This is evidenced by some automated reporting stations recording 0.25 inches per hour...and cold convective cloud tops appearing on IR satellite. Temps remain below freezing...so the bulk of this will fall as freezing rain. One benefit to the heavy rates is that some of this may run off before freezing as it comes down hard. I have extended some of the winter wx advisories for a few hours to cover some freezing rain while temps slowly tick up towards 32. The winter wx advisory for Knox and coastal Waldo has been cancelled as temps have warmed well into the 30s and low 40s. ORIGINAL DISCUSSION... Steadier precipitation has moved east into eastern Maine early this morning, with just some light freezing drizzle left in its wake. The next round of steadier precipitation is visible on regional radar imagery and should begin arriving in New Hampshire around 6AM and spread eastward through the morning. With cold air locked in place east of the mountains, this precipitation will begin as freezing rain for much of the area. One notable exception is northwest New Hampshire where downsloping conditions have kept temperatures above freezing most of the night (currently 39 at Whitefield). As surface low pressure forms and tracks east across southern New Hampshire, expect a warm front to lift northward ahead of it. This front will likely push north into southern to central New Hampshire as well as onshore in coastal Maine, with the low tracking eastward along it. To the north of the front it will stay cold, though temperatures may warm to near freezing within the dammed area as the steadier rain arrives. To the south of the front, temperatures will warm dramatically into the 40s to perhaps low 50s. Current Advisory headlines cover the expected threats today fairly well, with the timing still lining up well. Interior areas will hang on to the freezing rain threat into the afternoon while coastal and southern areas warm up earlier. Behind the warm front along the coast there could be some strong wind gusts with the greatest threat along the Midcoast where the Wind Advisory is in effect. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... As low pressure moves across the area it will drag a cold front across along with it. Winds will shift to the west behind it and expect precipitation to come to an end. Within the cold air dammed areas, temperatures behind the front will warm up, while other areas will see a gradual cooling with temperatures falling below freezing again Wednesday morning. Only minor warm up expected on Wednesday with cold air continuing to pour in. Winds may gust to 25 or 35 MPH as this cold air moves in. Will see some lingering snow showers mainly in the mountains, but these may spread east out of the mountains during the afternoon. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... The main concern for the long term portion of the forecast will be the system affecting New England next Saturday into Monday. Before that though, we will see a warming trend. At the surface, high pressure will translate east from the central CONUS Thursday and Friday before sliding offshore. Ensemble mean 850mb temps go from near -20C Thursday to around 0C by Saturday morning as a warm frontal boundary will be pushing into the region by late Friday night/Saturday morning. Southerly flow will transport in modified subtropical air. The operational Euro as well as the Canadian are slower with the weekend system and in better agreement with both the ECMWF ensemble system and also the GEFS members than the operational GFS. A slower eastward progression could mean more mixed precipitation initially and possibly the development of a coastal storm as the system would have more time to organize and deepen. This event could also have quite a bit of QPF with it, and this combined with warmer temperatures initially may once again bring a concern for ice jams and river flooding. On the backside of the system cooler air would begin to filter in with a cold frontal passage Monday, changing all precipitation to snow. Have edged closer to these ideas/the Euro solution for the extended forecast, however confidence is not high in any solution at this time. Temperatures look to stay below freezing through Saturday morning when the warm air advection arrives. Highs will be well above normal for the weekend in the upper 30s to near 50 before dropping again behind the cold front early next week. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... Short Term...IFR conditions expected most of the day today with light freezing drizzle in the morning, becoming steadier as the morning goes on. Temperatures warm above freezing in southern and western New Hampshire as well as coastal Maine this morning, while interior areas may see the freezing rain last into the afternoon. A cold front moves across the area this evening, bringing an end to the precipitation and a return to VFR conditions for most areas outside the mountains. Long Term...We'll see variable cloudiness initially Wednesday evening into Thursday for the mountains very VFR conditions develop. Elsewhere VFR will prevail through Friday with lowering ceilings and precipitation developing on Saturday in rain and snow. && .MARINE... Short Term...Southerly flow ahead of low pressure moving across northern New England today will likely reach gale force for much of the coastal waters. A cold front crosses the area this evening, bringing the southerly gales to an end as winds shift to the west. Cold advection on Wednesday will allow winds to strengthen again to 30 or possibly 35 KT. Long Term...Marginal SCA seas over the far eastern waters will drop late Wednesday night into Thursday morning...however winds will remain gusty through Friday morning. Higher seas and near gales will return Saturday in gusty SW flow. && .HYDROLOGY... With expected rainfall today the additional run off into area rivers largely affected by ice may lead to additional ice movement or ice jams. Any ice jams that form or move may lead to minor flooding. The Flood Watch covers the areas where this threat is greatest. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Flood Watch through late tonight for MEZ012-018>028. Winter Weather Advisory until 6 PM EST this evening for MEZ007>009-012>014-018>022. Winter Weather Advisory until 2 PM EST this afternoon for MEZ023>026. Wind Advisory until 9 PM EST this evening for MEZ027-028. NH...Flood Watch through late tonight for NHZ003>015. Winter Weather Advisory until 6 PM EST this evening for NHZ001- 002-004-006. Winter Weather Advisory until 2 PM EST this afternoon for NHZ003-005-007>015. MARINE...Small Craft Advisory until 11 PM EST this evening for ANZ153. Gale Warning until 11 PM EST this evening for ANZ150>152-154.