textproduct: Gray - Portland

WHAT HAS CHANGED

Snowfall amounts along the coast have increased quite a bit from the afternoon package as guidance continues to shift a strong low pressure system closer to the coast. NBM totals were bullish compared to current confidence levels. With a large model spread still present, this forecast reflects a more conservative solution.

KEY MESSAGES

1. Snowfall rates will decrease through the early morning with snowfall becoming more intermittent around daybreak. Accumulating snow likely ends after daybreak while slick travel will continue through the morning due to snow covered roads.

2. The odds for plowable snow along the coast are increasing as guidance continues to trend a strong coastal low closer to the coast. Additionally, a closer track would also bring elevated wind gusts and a threat for splashover/minor coastal flooding.

3. Models continue to hint at active weather through the end of the work week, with additional chances for widespread precipitation.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Low pressure roughly 200 miles ESE of Cape Cod will continue to trek east early this morning while an closed 500 mb low over Lake Ontario will transition to an open wave as slides overhead later this morning. Latest radar presentation shows show remnant banding features over western Maine are weakening with breaks in the snowfall pushing into south-central New Hampshire. Chances for snow will continue into 7 AM with additional with only light additional accumulation. Skies will clear from NE to SW this afternoon with highs ranging from the upper 20s across the north to the mid 30s south of the mountains.

KEY MESSAGE 2 DESCRIPTION... Bottom line up front: Models continue to shift a strong low pressure system closer to the coast. This brings increasing chances for plowable snow to the coast, with lighter but still measurable amounts to the remainder of the area. With a closer track we will also have to keep an eye on wind gusts and the potential for splashover and/or minor coastal flooding around the time of high tides. Here is where we stand with respect to each potential impact with the latest rounds of guidance:

Snowfall - The latest guidance has increased probabilities quite a bit from this time last night with the Euro ensemble now spreading 50-60% chances of greater than 6" from southern Hillsborough County up through the southern Maine coast. With a 70% chance over coastal Rockingham. The GEFS in agreement in southern New Hampshire, but surprisingly is not as bullish up the Maine coast. The NBM 25-75th spread remains large (5-25" along the immediate coast), but this combined with everything else does increase confidence in accumulating snowfall. As expected there is a very tight gradient as you move inland and this is where the most uncertainty currently lies. Both global model camps are showing near 100% probabilities of greater than 3", however the NBM spread remains large as we are now getting into the hi-res window and while models like the NAM bring widespread accumulating snow, the RRFS only brings it up to the foothills. In summary, confidence is increasing in the coastal plain seeing accumulating snowfall, with less confidence inland. Timing has also become clearer with snow likely not reaching our area until the early hours of Monday morning and lasting into early Tuesday. Amounts remain highly uncertain, but with hi-res models now in the mix we should be able to lock onto a more certain track over the next 24 hours.

Winds - Current global ensemble camps currently have a roughly 50- 70% chance of winds gusting to near 40 mph Monday afternoon and evening on the immediate coast line. The higher probability solution at this point looks like widespread 20-30 mph gusts with more frequent 30-35 mph gusts along the coast. For the waters there are reasonably high probabilities of storm force winds (55 mph or greater) and therefore a storm watch remains in effect. Similarly to the snowfall just a subtle shift in the track either way can change this.

Coastal Flooding - The latest surge guidance blend we have been using looks a little bullish to me and I think its a result of the ETSS which has been consistently running hot during storms. The astronomical high tide is around 10ft overnight Sunday when the system makes it's closest pass with surge models in good agreement of 2-2.5 ft of surge. However, the peak of this surge occurs just after the peak of the high tide cycle and therefore I am not too gung ho on advertising minor coastal flooding at this point, but I do think some splashover is possible with building nearshore waves. We will have to keep a close eye on this, because like the other impacts this one depends highly on the still uncertain track.

KEY MESSAGE 3 DESCRIPTION... We follow the early week system with mostly drier weather and seasonable temperatures, but models are hinting at some precipitation associated with a wave Wednesday night and then potentially something more significant toward the end of next week. Best to take it one storm at a time as the models do have trouble juggling multiple systems in close proximity to each other, but worth a mention to finish out the forecast period.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

Through 06Z Sunday...IFR to locally LIFR with continue in low ceilings and light snow until around 12Z. Snow mostly ends after 12Z with ceilings lifting through the morning. Conditions will improve to VFR from NE to SW through the afternoon with VFR likely into tonight.

Outlook...

Sunday: Mostly VFR

Sunday night-Monday night: VFR trending to MVFR overnight Sunday. By early Monday expect widespread MVFR with localized IFR restrictions as snow moves into the area. Currently confidence remains low in the extent of the snow, but coastal terminals have the highest potential. In addition gusty winds 25-30 kts are also possible at coastal terminals during this period.

Tuesday-Wednesday: Conditions trend back to VFR Tuesday as snow tapers off and ceilings lift and scatter out. VFR then prevails through Wednesday.

MARINE

Low pressure tracking east away from the Gulf of Maine will bring NE winds shifting N through the morning. Winds and seas will continue SCA conditions until early afternoon. Winds and seas will below SCA thresholds tonight into Sunday.

Wave heights and winds begin to pick up Sunday night as a strong low pressure system approaches the Gulf of Maine. By Monday winds may be up to storm force on the outer waters, with gales in the bay. Winds taper off to below 25kts by Tuesday afternoon. Seas top out at 12-15ft Monday night and slowly recede below 5ft by early Wednesday morning. A small craft advisory may be needed Wednesday night through Thursday night as another disturbance crosses the waters.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Winter Weather Advisory until 7 AM EST Saturday for MEZ007-008- 012-013-019>028-033. Winter Storm Warning until 7 AM EST Saturday for MEZ018. NH...Winter Weather Advisory until 7 AM EST Saturday for NHZ001>004- 012>014. Winter Storm Warning until 7 AM EST Saturday for NHZ005>011- 015. MARINE...Small Craft Advisory until 1 PM EST Saturday for ANZ150>154. Storm Watch from Monday morning through Monday evening for ANZ150-152-154. Gale Watch from Monday morning through Monday evening for ANZ151-153.