Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/16/17

Area Forecast Discussion

National Weather Service Gray ME

 1051 PM EST Wed Feb 15 2017

.SYNOPSIS...
Low pressure will rapidly develop in the Gulf of Maine tonight
and pulls away Thursday leaving behind upslope snow showers in
the mountains. High pressure will build into the region on
Friday as the storm departs to the maritimes. A few upslope snow
showers will linger in the mountains through Saturday but
elsewhere skies will be mainly sunny. Temperatures will warm
through the weekend reaching the mid 40s by Sunday.

&&

.NEAR TERM /THROUGH THURSDAY/...
1045 pm...Second band of moderate to heavy snow extends from
from around KLEW southward through the Portland area, and then
offshore of York and Rockingham counties. This band should
shift W through around 06Z or so before dissipating. Rates of an
inch an hour are likely in this band, and could see them as
high as 2" per hours. HRRR has been excellent with these bands
today and tonight. Will hold the WSW for now as we will see some
synoptic snow developing over the ern zones, but may be a
struggle to reach warning criteria here.

8 PM...Intense sfc convergence, along with mid lvl frontogenesis
have combines to produce a persistent band of heavy precip from
around Casco bay NW through Cumberland and southern Oxford
counties. We`ve had reports of 2-3" an hour for a couple hours
in this band. Just got reports in the last hour of a changeover
along the coast and in Portland, which will limit total snow
accums there. Forecasts for this evening lean heavily on meso
models, including HRRR, and meso model ensembles. This rotates
this band of heaviest precip SSE through York county/ including
NH border towns in Carroll county/ and then into Strafford and
Rockingham toward midnight. The band will weaken a bit later
this evening, so amounts to the south will probably not reach
the totals we`ll see in interior SW ME, but should still reach
warning criteria. This will also limit the snow to some degree
over ern zones, and may not see warning criteria here, but will
hold the warning to see how synoptic precip develops this
evening.


Previously...A dynamic storm is in store for this evening and
overnight. Temps have pushed into the mid and upper 30s over
parts of Srn NH and coastal Wrn ME. This has allowed precip to
start as rain. Farther inland snow has continued in the higher
terrain much of the day...with accumulations already around 6
inches.

Now things really start to get interesting. As mid level low
centers rapidly develop this evening...colder air will be
dragged back S thru the forecast area. This will turn any rain
back to snow. KGYX 88D dual-pol data is already showing low ZDR
and high CC values collapsing back towards the coast as heavier
areas of lift and precip move thru. At GYX we flipped from light
rain to heavy snow in a matter of minutes as stronger lift moved
overhead. I expect this to be the trend thru the evening...with
mixed precip transition quickly to heavy snow with rapid
accumulations. The coast will be the last place to flip back to
snow...but when it does it will be a significant hazard for
those on the road. Roads will become slippery in a hurry.

The surface trof remains wedged at the NH/ME border back towards
the White Mtns. I expect it to hold more or less stationary thru
the early evening. For that reason I have focused the higher QPF
across extreme SWrn ME into the White Mtns. Later this evening
strong low pressure developing in the Gulf of ME will drag
this trof Swd. This should be when the heaviest snow occurs for
Srn NH. It may not last more than an hour or two...but snow
could be very heavy for that short duration. For the rest of the
night intensity of snow will taper off but continue into
morning.

Headlines remain as they were earlier today. Highest snowfall
amounts should be near the NH/ME border...especially where SE
facing upslope assisted in lift. The lowest confidence in
snowfall amounts are just W of the current trof axis...where
shorter duration of snowfall may limit totals some. Also to the
E over central ME...lower snowfall totals are possible due to
mixing and lack of precip. Their best snowfall may come later
tonight when low pressure begins to throw moisture back NWrd.
The very mesoscale nature of this event will lead to some wildly
varying snowfall amounts over short distances.

&&

.SHORT TERM /THURSDAY NIGHT/...
Low pressure will gradually pull away from the area Thu.
Lingering low level moisture and NW flow will lead to plenty of
upslope snow showers in the mtns thru the day. An additional
several inches of accumulation is possible. We stay in cyclonic
flow Thu night...and that should keep the boundary layer fairly
mixed. I stayed close to 2 m temp guidance for lows.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
High impact weather potential: None

A rather quiet period of weather as we move into the end of the
week and the weekend. The forecast begins with a relatively
progressive high amplitude pattern over North American. As of
Wednesday morning a large ridge was build up through western
North American with above freezing surface temperatures all the
way to the Northwest Territories in in Western Canada, and a
trough moving through New England and southern Quebec. This
ridge will move east over the weekend keeping high pressure in
control through the start of next week.

Friday the departing low will bring upslope snow showers to the
mountains of northern New Hampshire. Have increased QPF and snow
amounts slightly compared to guidance as those areas are often
able to squeeze quite a bit of snow out of this pattern.

Saturday a high builds into the region and temperatures will
warm above freezing across most of the area.

A weak system passing to the north on Sunday may bring a few
scattered flurries to the mountains and increasing clouds
however temperatures will again remain warm reaching the mid 40s
south to upper 30s north. Those flurries and clouds will stick
around into Monday.

By Tuesday there is the potential for another storm to bring
more widespread precipitation. Confidence is very low at this
time and have gone with a consensus blend of guidance.

&&

.AVIATION /04Z THURSDAY THROUGH MONDAY/...
Short Term...Widespread IFR or lower is expected tonight in deep
onshore flow. -RA along the coast will change to SN...heavy at
times. Eventually this may even clip CON and MHT...as snowfall
drops Swd tonight. Conditions improve to MVFR and VFR early
Thu...except in the mtns where SHSN will keep occasional IFR.
Surface gusts around 20 to 25 kts possible at all terminals Thu.

Long Term... VFR will prevail from Friday right through the
weekend except in the mountains where HIE will see periods of
MVFR in SHSN.

&&

.MARINE...
Short Term...Winds and seas will build especially behind rapid
strengthening low pressure in the Gulf of ME. Gale warnings for
the outer waters and SCAs for the bays remain in effect into
Thu. Winds and seas will gradually diminish as low pressure
pulls away.

Long Term... Very quiet period on the waters with high pressure
built overhead. Expect conditions to remain below SCA right
through the start of next week.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Storm Warning until 10 AM EST Thursday for MEZ012>014-
     018>028.
     Winter Storm Warning until 7 PM EST Thursday for MEZ007>009.
NH...Winter Storm Warning until 10 AM EST Thursday for NHZ004>006-
     008>010-013-014.
     Winter Storm Warning until 7 PM EST Thursday for NHZ001>003.
     Winter Weather Advisory until 7 AM EST Thursday for NHZ007-011-
     012-015.
MARINE...Small Craft Advisory until 10 AM EST Thursday for ANZ151-153.
     Gale Warning until 6 PM EST Thursday for ANZ150-152-154.

&&

$$
SYNOPSIS...Curtis
NEAR TERM...Cempa/Legro
SHORT TERM...Legro
LONG TERM...Curtis
AVIATION...Curtis/Legro
MARINE...Curtis/Legro




Area Forecast Discussion

National Weather Service Marquette MI

 658 PM EST Wed Feb 15 2017

.SHORT TERM...(This evening through Thursday)
Issued at 408 PM EST WED FEB 15 2017

WV imagery and RAP analysis indicated an amplified pattern with a
ridge from srn CA to central Canada and a trough from Quebec into
the northeast CONUS resulting in nrly mid/upper level flow through
the wrn Great Lakes. At the surface, a ridge from nw Ontario through
ern MN was slowly building to the east as nnw flow LES continued
across Lake Superior.

Tonight, as the ridge builds into the area and the winds diminish,
the higher res models suggest that lake induced troughing and
land breezes will focus the LES bands into the n cntrl cwa and
along the shoreline near Marquette by late tonight. With -16C
temps at the top of the 3k ft inversion, expect mainly light snow
showers but with high SLR values aoa 30/1 with the shallow
convective cloud in the DGZ.

Thursday, expect any remaining LES to diminish during the morning as
the ridge builds into the ern cwa and winds become offshore.
Otherwise, mainly cloudy conditions will prevail with low level
moisture remaining below the lowering inversion. Highs will range
from the lower 20s east to lower 30s west.

.LONG TERM...(Thursday night through Wednesday)
Issued at 249 PM EST WED FEB 15 2017

Real good agreement in the models and GEFS ensemble that upper ridge
over the western Conus builds across central Plains and Great Lakes
Fri into Fri night. Shortwave trough crossing northern Ontario on
Sat will flattern ridge slightly but it should build again Sun into
Mon with GEFS h5 heights and h85 temps both 2-3 standard deviations
above normal. Ridge will result in dry weather this weekend. Main
question will be how warm it will get Fri through Sun.

Latest NAM indicates increasing moisture 950-900mb (500ft-1500ft
agl) as early as Fri and certainly by Sat. Just not sure if this is
realistic or an artifact of models trying to generate too much low-
level moisture due to warming temps and expected melting snow.
Previous GFS runs were showing similar idea with low-level moisture
but 12z run looks more realistic with minimal moisture. With ridge
overhead, main low and cyclonic flow well to the north across
northern Ontario and sfc dwpnts Fri into Sat staying mainly below
freezing, have doubts that either day will have bkn-ovc low clouds
as NAM would indiate. Could see sct cumulus clouds though. Mixing to
925mb as soundings (even from the drier GFS) show seems too low with
upper ridge overhead and plenty of dry air in mid-upper levels. For
the warm Monday we saw earlier this week (set record high at NWS MQT
that day of 44F) the forecast soundings leading up to that day were
indicating similar scenario as NAM indicates on Fri and Sat (low
clouds and limited mixing height). Instead INL and GRB RAOBs at 00z
Tue indicated a mixing depth to 875mb to 850mb was achieved. Skies
were mostly sunny.

Though there was stronger mixing on Mon in lowest 5kft compared to
what should occur on Sat, think it could end up just as warm if not
warmer since h85 temps are much warmer (-2c on Mon and at least +8c
on Sat). Will continue to use 900mb temps as gage for high temps
which supports highs Fri mainly in the 40s and mainly in the upper
40s to middle 50s Sat and Sun. Since is it forecast to be drier in
low-levels on Sun that day may end up the warmer day. Lake breezes
are possible either day which would result in falling temps in the
aftn locally near the Great Lakes. Overall this weekend will feel
more like spring instead of winter. Record highs this weekend are
mostly in the 50s to low 60s. Here is a sampling of the record highs
for Fri 2/17 through Sun 2/19. Record highs seem possible.

Ironwood: 2/17 is 60 (2011), 2/18 is 58 (1981) and 2/19 is 60 (1930)
 Irn Mtn: 2/17 is 58 (1981), 2/18 is 51 (1930) and 2/19 is 62 (1930)
 NWS MQT: 2/17 is 61 (1981), 2/18 is 52 (1997) and 2/19 is 46 (1988)
Mqt city: 2/17 is 55 (2011), 2/18 is 52 (1954) and 2/19 is 62 (1930)
Newberry: 2/17 is 47 (1954), 2/18 is 46 (1997) and 2/19 is 47 (1994)

Shortwave trough moving over the Pacific Northwest later this
weekend deepens as it tracks across the northern Plains on Mon and
over the Great Lakes Mon night into Tue. Sfc trough over the plains
on Mon deepens to 995-1000mb low while lifting across northern
Ontario by Tue morning. With enough morning sunshine on Monday could
see temps again rise well into the 40s if not reach the 50s. Clouds
should thicken later in the day though as shortwave comes closer.
Upper Great Lakes will be well within warm sector of this system on
Mon night with h85 temps up to +10c and sfc dwpnts rising toward
40F. SW H85 winds over 50 kts will pump PWATs over 1 inch or roughly
4-5 standard deviations above normal. The abundant deep moisture
should help to develop rain showers over Upper Michigan late Mon
into Mon night. Timing still varies, though would expect a period of
rain sometime from late Mon aftn through daybreak on Tue. Given
strength of theta-e ridge just upstream and moisture advection
suppose there could also be thunder. Sfc dwpnts over 40F advecting
over the melting snowpack could result in areas of fog Mon night.
Sfc trough crossing the area on Tue morning will shift winds to the
W or NW pushing a drier and cooler airmass across Upper Michigan
through the day.

Tue into Wed the shortwave trough will head east across Quebec and
New England while weakening. Upper flow will become more zonal again
which casts doubt on the cold air that was showing up for mid to
late next week in model runs 24 hour ago. GFS remains cooler than
ECMWF and GEM especially for middle of the week, but consistency in
the ECMWF and GFS runs is lacking. Will leave consensus for now
given the poor run to run continuity, but overall think models are
heading toward zonal pacific flow pattern with temps at least
slightly above normal.

Beyond the end of the long term, recent runs of GFS and ECMWF
including latest runs hint at stronger storm system over ncntrl
Conus late next week (24-25 Feb). That system could bring snow to
portions of northern Plains and snow and/or mixed precipitation
across Upper Great Lakes.
&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 631 PM EST WED FEB 15 2017

Lake effect snow showers have diminished this evening and are now
only affecting KSAW while light snow approaching the western U.P
has also diminished as it moved into the drier air mass in place
over the area. Look for MVFR conditions at all the TAF sites to
improve to VFR later this evening/overnight as drier air continues
to diminish -sn and erode lower cloud cover. &&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 408 PM EST WED FEB 15 2017

With high pressure building into the region, winds to around 25
knots over the ern lake will continue to diminish tonight. Winds
through the weekend will remain at or less than 25 knots as the
pressure gradient remains week across the area in the absence of any
major pressure systems.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...JLB
LONG TERM...JLA
AVIATION...Voss
MARINE...JLB