Historic Early May Snowstorm Update One

000
FXUS61 KCAR 090547
AFDCAR

Area Forecast Discussion
National Weather Service Caribou ME
147 AM EDT Sat May 9 2020

.SYNOPSIS...
Low pressure will reach the Gulf of Maine overnight, then exit
across the Maritimes Saturday through Sunday. Another low will
intensify across the Maritimes Monday night into Tuesday then
move slowly northeast over the open North Atlantic Wednesday.
&&

.NEAR TERM /THROUGH TODAY/...
Update...
Intensifying low pressure will track from southern New England
to the Gulf of Maine overnight. Precipitation will expand north
across the forecast area in advance of the low. Across Downeast
areas precipitation will be in the form of rain and snow, with
snow across the remainder of the forecast area. Overnight snow
accumulations will generally be around an inch or less. Low
temperatures will range from the mid 20s to around 30 north, to
the lower to mid 30s interior Downeast with mid to upper 30s
along the Downeast coast. Have updated the forecast to adjust
for current conditions along with overnight temperatures and
precipitation chances/types.

Previous Discussion...

     Unusual Significant May Snow Event...

Otherwise, all Models have come arnd to the idea of a little
more deepening with the mid Atlc sfc low as it enters the Gulf
of ME late tngt, then tracking near Eastport ME erly to mid Sat
morn then into Nern NB prov by late Sat aftn. More importantly,
is the potential development of a sig 700-500mb closed low ovr
Ern ME and Wrn NB by Sat aftn, enhancing the potential of a sig
deformation sn banding from late morn into Sat eve, with banding
becoming tangential to the Ern ME/NB border from about Danforth
nwrd durg the ht of the event. We used thresholds of 35 deg or
less for all snow and 39 or less for rn and sn mixed with this
event with cold air alf with this event no problem, with the
deepest upper low and coldest air alf obsvd since the upper air
era began circa arnd 1940. You would have to look up analogs
from David Ludlam`s "Early American Winters" to get better sfc
description analogs of similar events this late in spring durg
the "Little Ice Age" periods.

Precipitation will begin mixed ovr interior Downeast areas and
rain ovr coastal Downeast areas ovrngt and sn ovr Cntrl and Nrn
areas late tngt or erly Sat morn. Aftwrds, its all about where
the best sn banding sets up and higher trrn, where fcst model
soundings indicating the best lift co-located with the
dendritic growth zone durg the deformation band stage. So it
all comes down to how hard it can snow durg the aftn hrs to
overcome powerful May background radiation. Sn ratios were
factored by whether precip was categorically all sn, the tm of
day, and by elevation, where trrn above 1000 ft msl was given sn
ratios closer to or even abv 10:1 given favorable crystal growth
modified by wind. In order to get reasonable event scenario hi
temps Sat across the fcst area, we had to defer to hrly GFS
model temps, then derive the fcst hi temps by adding one deg F
to the warmest hrly temp at each lctn. This resulted in
unseasonably cold, and likely record cold daily max temps for
most lctns.

We are not completely without precedent regarding accumulating
daytime May snfl, with an analog of a smaller scale event that
occurred ovr NE ME on May 16th, 2016 where sn that began erly in
the morn hrs was able to cont to accumulate into the erly aftn
hrs with mdt to hvy sn rates. This event seems to be at least if
not more favorable over a larger area of the FA.

The break out of Eastern Aroostook county was partly based on
impact, this being an unusually late season event, where heavy
wet snow will likely be followed up by strong winds on the back
side of the departing low with amts a little less than our
normal wntr stm criteria and of course the potential of lcly
heavier snfl meeting or exceeding criteria under any strong
banding. Stm total snfl this update is between the the 35th and
50 percentile of sn probs from supporting model ensmbls, with
the reference of locally high sn totals with banding in the 50th
to 75th percentile.

Steady sn or mixed sn/rn will end earliest ovr SW ptns of the
FA by erly eve, and last ovr the NE late Sat tngt with the slow
exit of the deformation band there with sct sn shwrs left
aftwrds with strong llvl cold advcn favoring sn shwr streamers
from the St Lawrence seaway. We have not mentioned any blsn
across the N attm for Sat ngt, but given gusty NW winds we
cannot rule it spcly where snfl is a little more fluffy ovr
cooler hi trrn lctns.
&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...
Winds and cool temperatures are the primary concerns for Sunday.
Highs will only be in the low to mid 40s north and near 50F for
Bangor and Downeast. This is well below normal. A deep mixed
layer will generate low dew points and very gusty west winds.
Wind chills on Sunday will be in the upper 20s to 30s. Winds
will gust as high as 35 to 40 mph. Can`t rule out a few showers
in northern zones, but don`t expect measurable precip. The
winds calm down for Monday and temperatures will rise into the
50s for the area. Some clouds can be expected later in the day
in the southern half of the area with a chance of showers. Have
gone with a more southern path for a shortwave propagating out
of the Ohio River Valley into southern New England. The 08/12Z
ECMWF seems to be the most aggressive solution, but went with a
broad blend of models that keeps precip confined mostly to the
Downeast region. The low does appear poised to deepen
significantly as it passes south of Maine Monday night and will
have to be closely monitored for a more northward path...as more
snow could result.
&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
The storm system will continue deepening in the Maritimes on
Tuesday. Did maintain some PoPs in Washington County early
Tuesday, and as mentioned above, will have to watch for a more
northern track which would increase PoPs through Tuesday morning
with that threat of another round of snow like the back to back
May storms in 1967. Confidence is high in another windy and
unseasonably cold Tuesday with highs in the 40s to low 50s and
northwest wind gusts over 30 mph again. Adjusted dew points
downward and winds upward for Tuesday afternoon due to a deep
mixed layer. This trend continues for Wednesday. Diurnally
driven cu/stratocu field can be expected over the entire area
with temps just slightly warmer than Tuesday. Winds finally let
up for Thursday with temperatures creeping towards seasonable
levels Thursday into Friday. There is another storm system
showing up on the charts late week with the usual wide variety
of model solutions. Will go with chance PoPs at this point with
the expectation that the system will slide to the south.
&&

URGENT - WEATHER MESSAGE
National Weather Service Gray ME
824 PM EDT Fri May 8 2020

MEZ012>014-018>028-033-NHZ004-006-008>015-090900-
/O.NEW.KGYX.WI.Y.0007.200509T1400Z-200510T0100Z/
Southern Oxford-Southern Franklin-Southern Somerset-Interior York-
Central Interior Cumberland-Androscoggin-Kennebec-Interior Waldo-
Coastal York-Coastal Cumberland-Sagadahoc-Lincoln-Knox-
Coastal Waldo-Interior Cumberland Highlands-Northern Carroll-
Southern Carroll-Merrimack-Belknap-Strafford-Cheshire-
Eastern Hillsborough-Interior Rockingham-Coastal Rockingham-
Western And Central Hillsborough-
Including the cities of Bethel, Bryant Pond, Hanover,
Locke Mills, Milton, Newry, Rumford, Norway, Fryeburg, Oxford,
Farmington, New Sharon, New Vineyard, Temple, Wilton,
Chesterville, Jay, Athens, Cornville, Skowhegan, Palmyra,
Pittsfield, Embden, Madison, Hollis, Alfred, Lebanon, Sanford,
Goodwins Mills, Buxton, Limington, Berwick, New Gloucester, Gray,
North Windham, Gorham, Greene, Lewiston, Sabattus, Wales, Minot,
Turner, Auburn, Livermore Falls, Augusta, Sidney, Windsor,
Vassalboro, Waterville, China, Palermo, Brooks, Jackson, Knox,
Liberty, Montville, Morrill, Waldo, Winterport, Unity, Biddeford,
Saco, Old Orchard Beach, Kittery, Portland, Cape Elizabeth,
South Portland, Westbrook, Yarmouth, Brunswick, Arrowsic, Bath,
Phippsburg, Bowdoinham, Topsham, Bowdoin, Whitefield, Dresden,
Alna, Bremen, Bristol, Damariscotta, Newcastle, Boothbay Harbor,
Wiscasset, Waldoboro, Owls Head, Rockland, Appleton, Camden,
Hope, Rockport, Thomaston, Belfast, Northport, Searsmont,
Lincolnville, Bridgton, Harrison, Naples, North Conway, Albany,
Conway, Chatham, Crawford Notch, Wakefield, Bridgewater,
Brookfield, Ossipee, Tuftonboro, Wolfeboro, Moultonborough,
Boscawen, Canterbury, Concord, Dunbarton, Loudon, Hooksett,
Laconia, Gilford, Meredith, Barrington, Rochester, Dover,
Rollinsford, Somersworth, Durham, Madbury, Gilsum, Keene, Marlow,
Sullivan, Surry, Jaffrey, Manchester, Pelham, Nashua, Salem,
Atkinson, Newton, Plaistow, Chester, Derry, Hampstead, Exeter,
Greenland, Portsmouth, Rye, Hampton, Hampton Falls,
North Hampton, Seabrook, Amherst, Milford, Mont Vernon,
Goffstown, Peterborough, Sharon, and Weare
824 PM EDT Fri May 8 2020

...WIND ADVISORY IN EFFECT FROM 10 AM TO 9 PM EDT SATURDAY...

* WHAT...West winds 20 to 30 mph with gusts up to 50 mph
  expected.

* WHERE...Portions of central, northern and southern New
  Hampshire and south central, southwest and western Maine.

* WHEN...From 10 AM to 9 PM EDT Saturday.

* IMPACTS...Gusty winds could blow around unsecured objects. Large
  tree limbs could be blown down and power outages may result.
  Driving high profile vehicles may be difficult at times.

* ADDITIONAL DETAILS...Westerly winds will increase markedly mid
  morning through midday and continue through the afternoon hours.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Use extra caution when driving, especially if operating a high
profile vehicle. Secure outdoor objects.

&&
$$

MLE

:32 AM ADT Saturday 09 May 2020
Wind warning in effect for:

Halifax Metro and Halifax County West
Strong winds that may cause damage are expected or occurring.

Maximum gusts: westerly or southwesterly 70 to 80 km/h except 90 to 100 km/h along parts of the coast.

Locations: Digby county, Annapolis Valley, and the Atlantic coastal regions from Yarmouth County to Cape Breton County.

Time span: This evening until Sunday morning.

Damage to buildings, such as to roof shingles and windows, may occur. High winds may toss loose objects or cause tree branches to break.

Wind warnings are issued when there is a significant risk of damaging winds.

Please continue to monitor alerts and forecasts issued by Environment Canada. To report severe weather, send an email to NSstorm@canada.ca or tweet reports using #NSStorm.