Mesoscale Discussion 13

Issued

Jan 9, 2019, 4:25 AM EST (09:25 UTC)

Expired

Jan 9, 2019, 10:30 AM EST

In force

6 hr

Issued by

the Storm Prediction Center

Counties Franklin County, ME, Oxford County, ME, Belknap County, NH, Carroll County, NH, Coos County, NH, Grafton County, NH, Merrimack County, NH, Sullivan County, NH, Caledonia County, VT, Essex County, VT, Orange County, VT, Rutland County, VT, Windsor County, VT

The Burlington radar (KCXX), 118 km from the middle of the area, began a volume at 09:28 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

048 
ACUS11 KWNS 090926
SWOMCD
SPC MCD 090925 
MEZ000-NHZ000-VTZ000-091530-

Mesoscale Discussion 0013
NWS Storm Prediction Center Norman OK
0325 AM CST Wed Jan 09 2019

Areas affected...portions of VT...NH and western ME.

Concerning...Heavy snow 

Valid 090925Z - 091530Z

SUMMARY...A belt of increasingly heavy snow, with rates commonly 1-2
inches/hour and locally/briefly higher, should pivot across this
corridor from southwest to northeast through mid/late morning local
time.  Brief mixed precipitation, including light freezing rain, is
possible around the south and east edges.

DISCUSSION...A low/middle-level cyclone, manifest on the 9Z surface
chart by a binary low with diffuse pressure minima near PSF and SLK,
is expected to deepen and consolidate as it crosses southern VT/NH
through dawn, reaching the ME coastline near PWM around 12Z, then
moving slowly up the coast thereafter with continued deepening.  As
the low-level cyclone intensifies, mass response will likewise
strengthen, including the combination of elevated forcings in the
conveyor occupying its proximal northern semicircle.

Meanwhile, large-scale lift forced from higher aloft -- contributed
by both DCVA immediately preceding the mid/upper trough/low and
left-exit region of a cyclonically curved/eastward-shifting jet
streak south of southern New England, will contribute to deep
columnar cooling.  As evident in time series of forecast soundings,
this process will freeze layers above the surface (near 850 mb) that
initially are warmer than 0 deg C, effecting transition of sporadic
freezing rain on the eastern rim of the advancing precip area to
snow.  As deep-layer lift from multiple sources strengthens in the
dendritic-growth zone, snowfall rates should increase beneath the
laterally expanding and vertically deepening area of ice-phase
precip production.  Steep midlevel lapse rates within a column that
is saturated (or very nearly so) also may support development of
transient lenses of weak MUCAPE, supporting embedded convective
elements and locally contributing to short-lived bursts of snow
rates topping 2 inches/hour, especially at higher ground elevations.

..Edwards.. 01/09/2019

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...GYX...BTV...ALY...

LAT...LON   43907285 44307248 44757187 44927171 45147153 45277128
            45237085 44827013 44347010 43907047 43217150 43247297
            43477323 43907285

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The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.