Area Forecast Discussion
Issued by NWS Marquette, MI

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577
FXUS63 KMQT 200520
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
1220 AM EST Mon Feb 20 2017

.SHORT TERM...(This evening through Monday)
Issued at 303 PM EST SUN FEB 19 2017

Though not near as warm as what occurred on Sat, seeing yet
another warm Feb day. Readings so far have topped out in the mid
50s over interior west cwa (warm spot at 3 pm was 59 degrees at
Watersmeet) but with lighter onshore winds, temps over rest of cwa
have stayed in the upper 30s to lower 40s near the Great Lakes
and in the the mid to upper 40s elsewhere. Thicker mid clouds
affected area this morning and intervals of mid to high clouds are
poised to swing across this evening and overnight. Clouds are
streaming ahead of deepening trough and organizing sfc moving from
the northern Rockies to the northern Plains by Mon morning. For
tonight, kept lowest min temps tonight over interior central and
east closer to departing lighter winds/high pressure ridge. Light
south winds and moisture off Lk Michigan could lead to fog though
mid clouds should limit the potential for widespread or dense fog.
Different story over western cwa where south winds sharply
increase after midnight due to increasing southerly gradient btwn
the departing high and approaching low pressure system in the
plains. Still south winds should keep mins around 40F at IWD.

On Monday, clouds thicken from west to east and rain arrives late in
the day. Otherwise will be breezy and temps will still be above
normal. Warmest readings well into the 50s will be over west due to
warmer start and as S-SE winds downslope. Flow off the Great Lakes
elsewhere will result in highs in the 40s, though it could be as
warm as low 50s near WI border and as cool as upper 30s over far
east cwa. May see another day with record highs too as based on
current forecast, IWD (51 in 1961), CMX (47 in 1961), IMT (50 in
1961) and NWS MQT (44 in 2003) could all be close to seeing records
set.

Shortwave trough slides to Manitoba to Upper Great Lakes 18z-24z.
Main sfc low deepens blo 1000mb over central Manitoba by Mon
evening. Deep layer q-vector convergence spreads rain fm west to
east in the aftn. Large scale forcing is moderate strength but main
driver for rain will be strong 925-850mb moisture transport due to
SSW 50kt H85 wind and pwat over 1.25 inches aimed into scntrl cwa
21z-24z on Mon. Lowest SI/s are west of cwa closer to mid-level
drying which may steepen lapse rates. Given strength of moisture
advection with the strong h85 wind max cannot rule out rumble of
thunder. Main result from any instability will be enhancing rain
rates. Heaviest rain is expected just beyond short term so there is
more with the heavy rain and hydro issue potential in the long term
discussion.

.LONG TERM...(Monday night through Sunday)
Issued at 303 PM EST SUN FEB 19 2017

With a mean wrn trof/ern rdg upr pattern dominating until late this
week, a flow of Pacific air wl result in continued above normal
temps for Upr MI. There wl be several disturbances lifting out of
the wrn trof and impacting the Upr Lks as well during this time, so
overall pcpn should run above normal. The first of these pcpn events
later on Mon into Tue wl drop all rain. While limited mstr inflow wl
restrict pcpn associated with the passage of the next disturbance on
Wed, the stronger disturbance/deeper lo pres that are likely to
track thru the Great Lks late this week could bring some mdt-heavy
sn to at least portions of the cwa on Fri into Sat. Colder air and
some les wl return for next weekend behind this disturbance.

Mon ngt...Warm conveyor belt mstr ribbon/axis of pwat as hi as 1.25
inches/band of showers and categorical pops accompanying shrtwv/sfc
lo pres lifting newd thru nrn Manitoba/nw Ontario toward Hudson Bay
wl cross Upr MI on Mon ngt. While there could be a rumble of thunder
given the hi pwat/h85 temps as hi as about 9C in the evng, fcst
marginal h85-5 lapse rates no hier than about 6C/km and mucape no
more than 50-100j/kg warrant no mention of thunder in the grids. The
rain wl then end w-e with the arrival of vigorous deep lyr qvector
dvgc/subsidence/drying behind the exiting warm conveyor belt. With
the models fcstg as much 0.75-1.00 inch of rain over the se cwa as
sfc dewpts rise aoa 40, the impact of sn melt/runoff on area rivers
is a concern. Fortunately, area rivers are still running well blo
bankfull despite some recent warm wx, sn depths/water equivalent of
the sn pack are blo normal, and the heavier ra is more likely to
fall over the se where less sn lingers on the ground and terrain
influences are relatively minor. So hydro concerns appear limited
attm.

Tue...Although most of the medium range guidance indicate another
shrtwv embedded in the zonal flow alf wl move thru the Upr Lks, the
dryness of the llvls wl limit any impact to some mid clds. With h85
temps fcst as hi as 5-6C over the scentral, expect another day of
unseasonable warmth. Over the central where the llvl wly flow wl
downslope, max temps wl likely rise well into the 50s.

Tue ngt-Wed ngt...Another shrtwv emerging fm the mean wrn trof is
fcst to ride ewd thru the nrn Plains and acrs the Upr Lks during
this time. Recent medium range guidance shows some sgnft differences
on the handling/timing of this disturbance. Recent GFS runs, with
the support of the 00Z GFS ensemble mean and the 12Z NAM, have
consistently shown a faster system with a weaker sfc lo pres
tracking to the n of Upr MI, limiting the impact to some sct showers
over mainly the nrn tier with limited mstr inflow. Recent ECMWF and
Cndn model runs fcst a somewhat slower/deeper shrtwv tracking
farther to the s and more wdsprd/lgt-mdt pcpn under 12hr h5 hgt
falls aprchg 100m/upr dvgc in the left exit of supporting 110 kt h3
jet max. Given these persistent differences, wl rely on the model
consensus for this fcst period. With the arrival of some colder air
in the wake of the passing disturbance, any light ra could mix with
some sn on Wed ngt. But with h85 temps falling no lower than about
-10C over the Keweenaw by 12Z Thu in the presence of an incrsgly
acyc flow ahead of trailing sfc hi pres/under large scale subsidence
that wl lower invrn base under 5k ft agl, les potential appears
limited at best.

Thu...Although some light les is not out of the question as h85
temps dip as lo as -10 to -12C over the nrn tier, looks like Thu wl
be a mainly dry day with sfc hi pres rdg over the Upr Great Lks
under shrtwv rdging alf btwn the departing disturbance responsible
for the Wed pcpn and a deeper shrtwv lifting out of the mean wrn
trof.

Thu ngt into Sat...Focus for this time period wl be the potential
for a major winter storm associated with shrtwv/sfc lo pres lifting
out of the wrn trof and toward the Great Lks. The models have been
inconsistent at best on the timing/track/intensity of this shrtwv
and accompanying sfc lo pres. While the mean wrn trof/ern rdg and
negative tilt of the shrtwv lifting to the ne would favor a deeper
sfc lo pres moving farther to the nw and some mixed pcpn over at
least the se cwa, the 12Z GFS has trended toward a weaker sfc lo
moving farther to the se thru far srn Lower MI /similar to the track
shown by the 00Z GFS ensemble mean/ with the nw cwa on the edge of
the accompanying pcpn shield that would be all sn over the cwa. On
the other hand, the 12Z Cndn shows the sfc lo pres moving over the
se cwa /similar to the 00Z ECMWF/, with heavy pcpn over the entire
cwa until dry slotting diminshes the pcpn over the se on Fri ngt.
The new 12Z ECMWF shows a compromise fcst btwn these two solns and
would result in mainly sn except for the areas bordering Lk MI. If
the 12Z ECMWF is correct, the track of the h85 lo over the Bay of
Green Bay maintaining ccb over most of the cwa, sharp cyc upslope
nne flow/blsn on its nw flank, and total qpf as hi as about 0.65
inch would require some winter storm wrngs. Given these persistent
sgnft differences, wl cont to rely on the model consensus and
mention the potential for some mdt-heavy sn on Fri into Sat in the
HWO.

Sat thru Sun...Lingering synoptic pcpn associated with the exiting
larger scale disturbance/sfc lo pres wl transition to les in the
favored sn belts on Sat/Sat ngt with the arrival of mid lvl drying/
subsidence over a llvl cyc nw flow that advects h85 temps as lo as
-16 to -18C into the Upr Lks. Any les wl tend to diminish later on
Sat ngt into Sun as trailing sfc hi pres moves into the area.
&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1216 AM EST MON FEB 20 2017

Expect VFR conditions into early aftn at KIWD/KCMX/KSAW under an
overall dry air mass. Conditions should deteriorate with the
arrival of a low pressure trough and rain showers late aftn into
evening. Conditions should drop to MVFR from west to east during
the afternoon. Cigs should drop into the IFR range this evening
with some LIFR conditions possible.

A tightening pres gradient and resulting increasing winds above a
low level inversion will lead to LLWS at KIWD overnight and even
though it will be during the day, persistent strong low-level
inversion will expand the LLWS potential to KCMX and KSAW later today.

&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 303 PM EST SUN FEB 19 2017

Winds stay 25kt or less into Mon morning (strongest over far west
near Duluth) then as low pressure deepens northwest of Lk Superior
into Mon evening, SE winds increase to 30 kts Mon aftn with gales 35-
40 kts late Mon aftn into Mon evening over much of eastern and north
central Lk Superior. Gale warning has been issued. Winds should then
stay mostly 25kt or less Tue thru Thu. Stronger winds, perhaps
gales, are expected Fri into Sat as a low pres system tracks ne thru
the Great Lakes region.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Warning from 4 PM this afternoon to 1 AM EST Tuesday for
     LSZ264>267.

Lake Michigan...
None.
&&

$$

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



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