textproduct: Gray - Portland

WHAT HAS CHANGED

Little has changed in the short term other than the expansion of of the winter weather weather advisory to portions of southern NH for early this morning as areas of freezing drizzle may cause slippery spots.

KEY MESSAGES

1. Some slippery spots likely for this morning's commute, mainly where surfaces are untreated. Thereafter, a rather gloomy day takes shape before we warm up for Sunday.

2. Spring-like warmth to start next week, inducing rapid snow melt and a low chance for river flooding.

3. The next chance for widespread precipitation returns the second half of next week with temperatures returning closer to seasonal normals.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Cold air damming will hold on early this morning allowing for areas of freezing drizzle. Therefore a winter weather advisory remains in effect early this morning for many areas for the potential for slippery spots. Fog will likely develop later tonight and last through this morning in spots as the moist low level air mass lingers.

Thereafter, we expected a mostly cloudy day today with warmer temperatures, but still a bit cool with areas of fog. The cold air damming will likely hold tight in much of Maine, keeping temperatures lower there than across western NH where a warm-up should commence.

A cold front approaches tonight with showers likely. Temperatures will have warmed up enough to allow for plain rain all zones. Lapse rates in the mid levels become steep, so a few thunderstorms cannot be ruled out, especially across western and northern zones.

We return to dry weather on Sunday with highs well into the 50s.

KEY MESSAGE 2 DESCRIPTION...

The upper-air pattern shows a 500 mb ridge cresting over New England the first half of next week as a trough begins to dig towards the region out of the Upper Midwest. This puts the region in a warm air advection pattern, and will bring a long awaited taste of true spring warmth to the region. However, how warm exactly it gets still remains to be seen.

850 mb temperatures are generally between 5-10C on Monday and 3-8C on Tuesday. From yesterday we have seen a bit of an upward trend for Monday while Tuesday has trended modestly cooler. The depth of mixing also looks more limited on guidance which should put a cap on how warm it gets but at minimum 50s look likely with the potential for 60s across the lower elevations of S NH and SW ME. One wildcard to watch will be a bit of a backdoor cold front on Tuesday which may result in cooler temperatures across the northern mountains.

The sudden warm up is likely to result in significant melting to the snow pack and some river ice movement. One note is dew points stay rather low which should keep the rate of melting in check, as well as no precipitation through Tuesday.

KEY MESSAGE 3 DESCRIPTION...

Widespread precipitation chances return on Wednesday as a cold front approaches and we start the day in low amplitude southwest flow aloft. Widespread cloud cover/precipitation along this front will likely work to keep temperatures on the cooler side of the guidance. The current 25th to 75th NBM percentile high temperature spread at GYX on Wednesday ranges from 39 to 52 so it seems like the ensembles are struggling to resolve many of the finer details this far out. Given pattern recognition, I lean towards the cooler side of the guidance for temperatures Wednesday and Thursday.

Precipitation chances will increase starting early in the day on Wednesday as a surface low deepens to our west along the approaching cold front. Some guidance then has a secondary low forming along the front and lifting up into our area on Thursday. The latest cluster analysis suggests that the strongest synoptic forcing will remain over Canada and northern Maine, but there will be enough lift along the front to produce widespread precipitation through the end of the week. While it's still too far out to speculate on precipitation type, it mainly looks like rain with snow mixing in for now. That being said, a fair amount of ensemble members would lead to some freezing rain and/or sleet mixing in at times so it will certainly be a time frame to watch closely.

Looking beyond, the active signal continues in much of the long term ensemble guidance.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

Widespread IFR or lower conditions are expected south of the mtns for much of today. Freezing drizzle will also be possible at all TAF sites until temps begin to warm early this morning. HIE may remain VFR or MVFR as low cloud cover struggles to make it past the mtns. Showers and lower conditions likely at times tonight. Becoming VFR Sunday, except in the mtns where MVFR CIGs may linger. Westerly surface gusts to 25 kt possible in the afternoon. Widespread enhanced low level wind shear will also be possible late this afternoon through tonight.

Outlook:

Sunday night-Tuesday: VFR conditions expected.

Tuesday night: Conditions becoming MVFR/IFR as rain and snow move into the area overnight.

Wednesday-Wednesday night: MVFR/IFR conditions continue. There is uncertainty in precipitation type for this time period, so widespread IFR is not out of the question if the forecast trends colder and terminals see more of a mix or snow.

MARINE

Short term...SCA has been extended into Sunday for winds and seas. SCA conditions may linger outside of the bays through Monday before starting to diminish at night.

Long term...Wave heights will remain around 5-6ft into early Tuesday morning but we will likely see a break in SCA conditions later Tuesday morning through Tuesday night. Winds and seas then ramp up again Wednesday as a disturbance moves through the Gulf of Maine. There is even some suggestion that gale force gusts may be possible at times through Thursday. Seas remain high with gusty winds through Friday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Winter Weather Advisory until 10 AM EST Saturday for MEZ007>009-012>014-018>022-033. NH...Winter Weather Advisory until 10 AM EST Saturday for NHZ001>006-009. Winter Weather Advisory until 5 AM EST Saturday for NHZ008-010- 012-013-015. MARINE...Small Craft Advisory until 5 PM EST Sunday for ANZ150-152>154.