Area Forecast Discussion
Issued by NWS Marquette, MI
FXUS63 KMQT 201948
Area Forecast Discussion
National Weather Service Marquette MI
248 PM EST Mon Feb 20 2017
.SHORT TERM...(Today and tonight)
Issued at 508 AM EST MON FEB 20 2017
Water vapor imagery and RAP analysis show a shortwave trof
swinging out over the western High Plains. Downstream, an
amplified ridge extends n-s across the western Great Lakes region
with 500mb heights currently 2.5 standard deviations above the
long term mid/late Feb avg. Increasing moisture transport ahead of
the trof is leading shra/tsra expanding n from TX n thru eastern
KS. Farther n, some shra/tsra are also developing over western and
central MN. Across Upper MI, it`s been a quiet night with just
sct-bkn mid and high clouds. Early morning conditions are again
unseasonably warm with temps ranging from roughly the mid 20s to
lwr 30s east half to as high as the mid/upper 40s far w around
KIWD under downsloping se winds.
Models have been very consistent for several days on the progress
of the upstream trof as it swings ene, reaching the western Great
Lakes late tonight. Strong moisture transport as warm conveyor
moisture ribbon shifts across the area along with deep layer
forcing and rather sharp low-level trof will yield shra that will
spread across the area w to e this aftn/evening. Shra will then
end w to e overnight as pronounced low-mid level dry air surges
into the area in the wake of the trof, though some -shra may
linger into Tue morning over the far e. Precipitable water is
still fcst to increase to a little over 1 inch within the warm
conveyor which would be record territory as sounding climatology
for Green Bay shows that a precipitable water value over 1 inch
has never been recorded in Feb. As a result, there certainly could
be some hvy downpours given the anomalously high precipitable
water values. Also, even though showalter index never falls blo 0C
and there is very little elevated instability, not out of the
question that there could be a few rumbles of thunder with 50+kt
low-level jet shifting across the area.
In general, expect pcpn amounts of around one-half to three-
quarters of an inch with potential of isold higher amounts.
Shouldn`t result in any stream/river hydro issues. However, if
some hvy shra occur with decent pcpn rates, there will be ponding
of water on roadways in low areas. Other roads could be affected
by ponding water if storm drains have issues with snow/ice.
Se winds off the Great Lakes today should keep temps down into the
40s across the Keweenaw and roughly the e half of the fcst area.
Some lakeside locations with direct flow off the water will stay
in the 30s. The western fcst area will see temps rise above 50F,
even mid to possibly upper 50s in locations with best downsloping
under se winds. Mins tonight will be above normal high temps at
this time of year, ranging from the mid 30s to around 40F.
.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
.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 508 AM 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
strengthening se to s winds today thru this evening. Expect winds
to reach gales of 35-40kt this aftn 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
Gale Warning until 1 AM EST Tuesday for LSZ265>267.
Gale Warning until 1 AM EST Tuesday for LSZ264.