Area Forecast Discussion
Issued by NWS Marquette, MI

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946
FXUS63 KMQT 202057
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
357 PM EST Mon Feb 20 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 356 PM EST MON FEB 20 2017

Strong upper trough is pressing across northern Plains with sfc low
lifting over southern Manitoba. Strong moisture advection with pwats
over 1 inch (a whopping 300-400+ percent of normal) surging in ahead
of the sfc trough is resulting in widespread showers and a few
clusters of tsra lifting toward Upper Michigan from the central
Mississippi river valley. RAP and HRRR matching reality well and
show showers moving over western cwa through late this aftn then
spreading to central cwa this evening and into far east cwa by late
evening. Have seen isold lightning strikes every now and then with
showers over eastern IA into western WI where RAP and NAM showed
elevated MUCAPE up to 100j/kg and based on the forecast instability
this evening could see isold tsra potential this evening as showers
slide across. Given the unusually high moisture lifting in and
the elevated instability could see heavy downpours as the rain
moves through.

As shortwave lifts across Upper Great lakes and sfc trough crosses
the region, showers should shift steadily west to east across Upper
Michigan. High res guidance including the NAM, HRRR, RAP and NSSLWRF
indicate that there will be brief break with initial showers and
then there may be another push of showers move through on the sfc
trough axis. Given steeper h85-h5 lapse rates near 7c/km moving in
with surge of mid level drying think best chance of tsra could
actually occur 05z-07z Tue over west, 08z-11z Tue over cntrl and
over east cwa 11-13z Tue. Effective shear up to 50 kts with wbzero
heights lowering to 7k and 50 dbz height for 1 inch hail of lower
than 20kft suggests that if storms can form overnight, there would
be risk of hail.

On into Tue. Once showers and possible isold tsra exit eastern cwa
early in the day should see column dry out quickly from west to
east. Breezy on the Keweenaw and those stronger winds are sign of
better mixing depth that will spread over rest of cwa. As main
trough exits east, low-level winds will start out west then shift to
the southwest ahead of another weaker low pressure system sliding
over northern MN. Overall mixing to 900-875mb supports highs well
into the 50s over much of cwa expect where winds are onshore. May
even see readings top out in the low 60s for interior west and
central. For now, increased temps to near 60F to come more into line
with better perfoming guidance with recent warm spell. Any showers
with the northern MN wave should stay west of cwa through late in
the aftn.

Thus far with the warm up rivers have not responded much likely due
to gradual melt as nighttime lows have dipped near or blo freezing.
Rivers should respond tonight into Tuesday though more significantly
as mins tonight will remain above freezing and with rainfall and
melting snow tonight and since readings spike into the 50s on Tue.
Overall the rivers should see their greatest rises in the next few
days. At this time, significant hydro issues are not expected due to
lower river and stream levels, overall lower than normal amounts of
water equiavalent in the snowpack and generally quick moving
rainfall tonight with total qpf staying mainly less than 0.75 inch
in most areas. Still some unknowns though including extent of ice on
rivers. At the least with the rain and melting snow tonight could
see ponding of water in low-lying/poor drainage areas, especially if
there is any ice/snow plugging up storm drains. Will mention this
potential in HWO.

.LONG TERM...(Tuesday night through Monday)
Issued at 246 PM EST MON FEB 20 2017

Beginning Tue night...A weak shortwave moving through the area and
the presence of a frontal boundary could produce some
sprinkles/drizzle over mainly the northern tier of the forecast
area. Otherwise, expect dry conditions.

Most of the models continue to trend stronger with a shortwave
moving through the area late Wed into Wed night. The 12z NAM and
ECMWF favor a sfc low track over the western CWA which makes
sense given the trend toward a stronger solution. The 12z GFS
meanwhile remains weaker and farther se bringing the swath of best
pcpn through Iron and Marquette counties.

If the western solution of the NAM/ECMWF does work out, not much
precip will fall across the CWA and it will be mostly confined to
the far west and the Keweenaw. Most of the pcpn would be rain or
a mix or rain/snow and possible fzra. Will have to watch this time
frame as there remains plenty of uncertainty.

Attention then turns to Fri into Sat as models continue to bring a
strong low pressure system SE of the CWA. While there continues to
be uncertainty on track/timing of the sfc low, there is a general
consensus that the low will track through central Lower Mi late Fri
into early Sat. Model disagreement may increase over the next few
runs as is normal in this scenario until the shortwave associated
with the system moves onshore late Wed. Given the current track of
the GFS, ECMWF and GEMnh, all or most of the CWA will see snow, with
moderate to possibly heavy snow over the north-central U.P. where
upslope and lake enhancement from h85 temps between -10 and -15c
will increase synoptic amounts. Blowing snow would also be an issue,
especially near Lake Superior. Will need to keep an eye on model
trends with this system over the next few days.

The weekend will see h85 temps continue to fall with LES likely in
the NW-WNW snow belts.
&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1249 PM EST MON FEB 20 2017

VFR conditions at KIWD/KCMX/KSAW under a lingering dry air mass will
give way to deteriorating conditions late this aftn into this
evening as shra spread w to e across the area with abundant moisture
surging n ahead of an approaching low pressure trof. Conditions
should fall to IFR at all terminals, even to LIFR at KSAW later
tonight as southerly upslope winds aid lowering of cigs. Even with
winds becoming gusty, persistent low-level inversion will allow for
LLWS into the late evening as strong low-level jet ahead of
approaching trof translates across the area. As trough passes
across there is signal emerging that there may be a one to two
hour period of isold thunderstorms so have included VCTS at all
TAF sites overnight. After trof passes tonight, there is uncertainty
in how quickly low clouds will clear out. With upslope westerly
winds, will plan for low clouds to hang on at KCMX thru the night.
KIWD should see low clouds scatter out, but best chance of
clearing will likely be at KSAW where westerly winds will
downslope. By mid morning on Tue, VFR conditions will dominate
with gusty westerly winds, especially at more exposed KCMX
location.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 356 PM EST MON FEB 20 2017

Tighening pres gradient btwn high pres ridge shifting toward the E
Coast and an approaching low pres trof will result in SE gales of 35-
40kt thru much of tonight across the e half of Lake Superior. Gales
will end with the passage of the trof late tonight. Winds should
then stay mostly 25kt or less Tue thru Thu. Stronger winds, perhaps
gales, are expected later Fri into Sat as a low pres system tracks
ne thru the Great Lakes region. After a hiatus from winter type
conditions, should also the potential for freezing spray return
later Fri into Sat.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Warning until 1 AM EST Tuesday for LSZ265>267.

  Gale Warning until 1 AM EST Tuesday for LSZ264.

Lake Michigan...
None.
&&

$$

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



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