textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes were needed with this forecast package.

KEY MESSAGES

1. An approaching cold front continues rain chances into this evening with a couple of gusty thunderstorms possible in southern NH.

2. A seasonably cold airmass and gusty winds arrive behind the cold front to start the weekend, with wintry conditions across the higher terrain.

3. Mild and dry conditions look to persist from Sunday through much of next week as high pressure dominates over the Northeast.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Surface low pressure will track roughly along or just south of the St. Lawrence River Valley and drag a strong cold front through New England this evening into tonight. Out ahead of the front, it's currently pretty dreary out in most places with overcast skies and fog, rain and drizzle. Temperatures have started to trend up slowly as southerly flow increases, and a warm front has made its way into southern NH, where temperatures have warmed into the lower 60s of 2pm.

The steadier rain is currently north across central and northern portions of the area, but looking upstream, more showers are on the way for later this afternoon and early evening as the cold front approaches. CAMS are showing a couple hundred J/kg of MUCAPE that may be sufficient for a couple of thunderstorms across the southern half of NH and into far southwest ME. Chances appear low, but if any storm that develops can become surface-based, there is enough wind shear for strong wind gusts. The better chance of this occurring is across southern NH, which SPC has placed in a Marginal Risk (level 1/5) of severe weather. Showers are expected to end from west to east this evening, and roughly another 0.10" of 0.25" precipitation between now and then.

KEY MESSAGE 2 DESCRIPTION...

Northwest winds become breezy behind the front late this evening and continue through tonight with gusts of 25 to 35 mph. Based on hi-res guidance, these breezy conditions should kick in late evening to around midnight. These winds will carry in a much colder airmass, and upslope mountains rain showers are expected to transition to snow showers overnight, which should continue into at least the first part of Saturday. Increasing Froude numbers tonight/early Saturday could result in some clouds and possibly a couple of rain or snow showers spilling over downwind of the mountains if we can hold onto enough low level moisture. The combination of temperatures falling into the 30s to low 40s and gusty winds will make for wind chills in the 20s and 30s toward daybreak Saturday, possibly teens across the north.

Cold air advection continues into Saturday, making it feel rather blustery out. Temperatures only recover somewhat into the 40s south of the mountains, but breezy NW winds of 25-35 mph will keep wind chills mostly in the 30s. Across the north, winds chills are expected to stay below freezing through the day. One silver lining is that a push of drier air will bring mostly sunny skies downwind of the mountains by the afternoon while diminishing clouds/upslope precip in the mountains.

For hikers: Conditions will be dangerous and wintry in the higher terrain. In addition to snow showers, winds will be much higher and and temperatures much colder, making for winds chills in the single digits to possibly below zero above tree line.

Winds will diminish Saturday night as high pressure builds overhead, bringing favorable conditions for radiational cooling. I've gone a cooler than the NBM on low temperatures with most of the area seeing lows in the 20s and possibly teens in the the northern valleys.

KEY MESSAGE 3 DESCRIPTION... High pressure crests overhead on Sunday which should allow for a warmer feeling day as winds calm. Under full sun we should be able to mix into the low 50s south of the mountains, and into the mid to upper 40s to the north. Clear and calm conditions continue into Sunday night setting up for strong radiational cooling. I have gone ahead and already started to capture that trend by blending colder MOS guidance into the NBM. The result is widespread temperatures in the 20s with only the immediate coast hovering near or above freezing.

The center of the high pressure moves off to the east Monday but for the most part should stay nosed in for the better the part of the day resulting in mostly clear skies and afternoon temperatures mixing into the mid to upper 50s for the majority of the area. At the same time low pressure develops off the coast of the Carolinas where it looks like it is going to meander into midweek. It may meander just far enough north Monday night to spread some high and mid-level clouds into the coastal plain and potentially up to the foothills. If it is just mostly high clouds we could see another night with decent radiational cooling, but if the trend continues to bring it further north and more midlevel clouds make it as well it will remain warmer. As a result we will roll with NBM for now which is a smattering of upper 20s to low 30s for much of the area, and upper 30s in southeastern New Hampshire.

High pressure begins to push low pressure back to the south during the day Tuesday which is going to bring about clearing skies, and probably the warmest day of the week with widespread low 60s. Seasonable temperatures and dry conditions then continue as high pressure crests over the region again Wednesday and lasts through at least the day Thursday. Late week there is some suggestion for another area of low pressure to interrupt the pattern again, but models are all over the place on where it forms and how it tracks, so it is really just worth only a brief mention until there is better agreement and/or a clear trend.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Through 18Z Saturday...Ceilings range from LIFR to MVFR this afternoon with showers and pockets of drizzle at times. A cold front will also bring a chance of thunderstorms, mainly for MHT, CON, and PSM. Winds turn west to northwest this evening behind the front, with conditions mostly returning to VFR, although occasional MVFR ceilings are possible overnight. The exception as always will be HIE, where MVFR ceilings remain likely with possible rain and snow showers overnight and into at least the first part of Saturday. Northwest winds will gust 25-30 kt tonight and Saturday morning, possibly up to 35 kt.

Outlook: Rest of Saturday: VFR with northwest wind gusts 25-30 kt, possibly up to 35 kt.

Saturday night: VFR with lighter winds.

Sunday-Wednesday...High pressure brings an extended period of VFR conditions with no sig wx. Wind will tend to follow typical diurnal patterns.

MARINE

Through Saturday night...SCA conditions continue through Saturday evening. South to southwest winds persist across the waters into early this evening ahead of a cold front but will quickly turn to the northwest later in the evening and into the early part of tonight behind the front. Brisk northwest flow continues on Saturday, and then winds become northerly and start to diminish late in the day as high pressure builds in from the west. Winds and seas further diminish Saturday night.

Sunday-next week...There is still some uncertainty regarding track of a low pressure system expected to develop off of the coast of the Carolinas next week. There is potential for this to push a 5 to 7 ft swell into the gulf of Maine for the first half of the week, but if high pressure remains dominant and this low remains suppressed conditions would likely be calmer. Late week is also uncertain as additional low pressure may form east of the Gulf of Maine.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until midnight EDT Saturday night for ANZ150>154.