Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 200900

Area Forecast Discussion
National Weather Service Burlington VT
400 AM EST Tue Feb 20 2018

Unseasonably warm, near record setting temperatures are
expected across the area through Wednesday along with periods of
showers or light rain. A cold front will swing south through
the area Wednesday evening with cooler temperatures in its wake
for late week. An active weather pattern continues into the
upcoming weekend with renewed chances for light rains and snows.


As of 245 AM EST Tuesday...The overall forecast picture remains
largely unchanged over the next 42 hours as a dominant +590 dm
subtropical ridge centered between Bermuda and the northern
Bahamas controls the deep-layer synoptic flow across the eastern
third of the nation. Deep southwesterly flow aloft will advect
an unseasonably mild airmass into the region beginning today and
persisting into early Wednesday afternoon. Numerous showers
with periods of light rain will continue across central and
northern counties today, lifting slowly north to the intl.
border and northward tonight into Wednesday morning as a strong
warm front lifts through the area. Back trajectory analysis at
500m suggests source air this afternoon originated across the
northern Gulf Coast States yesterday, with tomorrow`s air
wrapping around the ridge from the subtropical Atlantic near
Grand Bahama Island. With mean 925 mb temperatures surging above
+10C a period of extreme warmth by February standards will
evolve during the period. Highs today should mainly top out in
the 50s, with a few spot 60F readings in the southern St
Lawrence/Champlain Valleys and a few upper 40s in far
northeastern VT and near KMSS. Wednesday will be a record-
setting day as 925 mb temperatures surge into the +12 to +15C
range, pushing highs into the 60s to locally near 70F. If KBTV
can surpass 62F (I currently have a high of 69F) it will be the
second warmest February temperature on record, surpassed only by
the 72F set just last year! I wonder what the statistical odds
of that happening in the Queen City`s 134 year period of

As the temperatures warm a surge of higher dewpoint air, (upper 40s
to lower 50s) now poised off to our southwest across western NY/PA
will advect northeastward into our area fostering a period of rapid
snowmelt and robust river rises. By later Wednesday most, if not all
snow cover below 2000 feet should be essentially erased leading to
heightened concerns over ice breakup on area rivers. Given the broad
consensus in the guidance the Flood Watch remains in place with this
package (see hydro discussion below).

By Wednesday afternoon the surface boundary will swing southward
through the area as a cold front. The baroclinic zone with this
feature is quite sharp, so hourly temperature drops could be quite
noticeable within the hour of its passage (> 10F). Scattered to
numerous showers will drop south into the bulk of the forecast area
during this time, through trend more scattered in nature as one
progresses toward early evening winds veer to northwesterly.


As of 400 AM EST Tuesday...The cold front will exiting
southeast VT at the start of the short term period with any
lingering light showers tapering off by midnight. Despite strong
cold advection and temperatures falling into the 20s by
Thursday morning, rivers will be still running high and cresting
Wednesday evening but a few of the slower responding rivers may
still be rising overnight and not crest til Thu morning.

On Thursday, the frontal boundary becomes nearly stationary over
the mid-Atlantic region as it runs into the anomalously strong
ridging over the southeast. A weak wave aloft and surface low
will move along the front on Thursday and develop some light
overrunning precipitation with the west southwest flow aloft.
ECMWF, CMC, and SREF mean are furthest north and most bullish
on QPF with a tenth to quarter inch in southern VT and as far
north as MPV/BTV, while NAM/GFS keep it south of the region with
little more than flurries or sprinkles. For now just keeping a
chance of light snow or mixed wet snow/light rain in the
forecast with the split in the model solutions. Temperature
profiles mostly cold enough for snow though the lowest valley
locations may have some light wet snow or light rain mixed in
with high temperatures in the mid to upper 30s. Perhaps the
models will come into better agreement today.


As of 400 AM EST Tuesday...Slightly cooler but still warmer
than normal conditions will prevail through early next week. The
region will also remain in an active pattern with a fast WSW
flow aloft as southeast ridging continues to dominate aloft. The
first in a series of low pressure systems will bring a mix of
rain and snow to the region Friday afternoon into Friday night,
followed by another late Sat night and Sunday. Although there
are slight differences in the tracks of each of these lows,
overall it looks like temperatures will be cold enough for some
snow especially in the higher elevations and northeast VT, but
temperatures will be marginal so some valley mix or change to
rain look likely. Latest indications is the system on Sunday
might bring some stronger and gusty southeast winds. High
temperatures will generally be in the mid 30s to mid 40s with
lows in the 20s through the period. Later next week things look
quite interesting with the development of a blocking pattern
with cutoff lows and highs, something we haven`t seen in a


Through 06Z Wednesday...Latest Radar imagery shows rain filling
in across much of the forecast area with downslope winds keeping
KBTV VFR while the remaining TAF sites are a mix of IFR/MVFR.
Conditions will worsen through the overnight hours with the New
York TAF sites becoming solidly IFR through much of the daytime
tomorrow while northern and central Vermont remain largely MFR.
Heavier rain showers in the 14Z to 18Z time range may drop
KBTV/KPBG/KMPV briefly down to IFR ceilings and/or vis. Much of
the rainfall will move north into Canada by sunset and a
gradual improvement in conditions is expected through the late
afternoon and early evening hours but MVFR ceilings will likely
persist. A strong low level jet will tail the warm front as it
moves northward with most TAF sites seeing 35 to 40 kts of wind
shear from surface to 2kft tomorrow afternoon and likely
lingering through Wednesday morning.


Wednesday: Mainly VFR, with areas MVFR possible. Chance SHRA.
Wednesday Night: VFR. Slight chance SHRA.
Thursday: VFR. NO SIG WX.
Thursday Night: VFR. NO SIG WX.
Friday: VFR. Likely RA, Chance SN.
Friday Night: Mainly MVFR, with areas VFR possible. Chance SN.
Saturday: Mainly MVFR, with areas IFR possible. Chance RA, Chance
SHRA, Chance SN.


As of 245 AM EST Tuesday...A 42-hour period of anomalously warm
temperatures will affect the region through Wednesday
afternoon. Periods of rainfall, modest winds and dewpoint
temperatures climbing into the 40s to lower 50s will foster
rapid snowmelt and ice break-up across the entire area. Also
boosting confidence are extremely high thawing degree hour
totals - averaging 900 to 1200 over the period. The model
consensus shows rainfall totals averaging from 0.5 to 1.50
inches across far northern VT into the northern Adirondacks and
St Lawrence Valley with the highest totals in the latter
location. Lesser amounts generally under a half an inch are
expected across central and southern VT. Taking this all into
account, modest to substantial river rises look highly probable
starting this afternoon and continuing into Wednesday, supported
by NAEFS/SREF MMEFS hydrograph data. While widespread open
water flooding is not expected, several rivers may approach
minor flood including the Ausable R. at Au Sable Forks, NY,
Missisquoi R. at North Troy, VT and the Winooski R. at Essex
Junction, VT. More importantly, numerous ice jams remain in
place from the substantial thaw this past January so the
potential for localized high water and/or flooding near these
features remain a real threat as ice break- up occurs.


Here are the current record high temperatures for February 20th
and 21st:

Record High Temperatures:

     ............Feb 20th....Feb 21st....
BTV.............58 (1981)...59 (1981)...
MPV.............56 (1994)...57 (1953)...
MSS.............63 (1994)...62 (1953)...
St. Johnsbury...60 (1981)...62 (1981)...

Record High-Minimum Temperatures:

     ............Feb 20th....Feb 21st....
BTV.............50 (1981)...49 (1981)...
MPV.............47 (1981)...47 (1981)...
MSS.............47 (1994)...41 (1981)...
St. Johnsbury...40 (1981)...46 (1981)...


VT...Flood Watch through Wednesday evening for VTZ001>012-016>019.
NY...Flood Watch through Wednesday evening for NYZ026>031-034-035-


LONG TERM...Sisson
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