Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 291848

Area Forecast Discussion
National Weather Service Marquette MI
248 PM EDT Wed Mar 29 2017

.SHORT TERM...(This evening through Thursday)
Issued at 247 PM EDT WED MAR 29 2017

12Z raobs/latest wv imagery and RAP analysis show a split flow
dominating NAmerica, with upr rdging in both the nrn and srn streams
supporting Hudson Bay hi pres centered over nw Ontario extending a
sfc rdg axis into the wrn Great Lks. Despite the presence of this
rdg axis over Upr MI and some dry llvl air shown on the local 12Z
raobs, quite a bit of hi cld streaming to the ne fm closed srn
branch lo over the srn Plains has overspread the area as winds
aloft shift to the sw ahead of a nrn branch disturbance near the
Cndn border moving e thru the Plains. Pcpn on the ne flank of the
srn branch closed lo has moved as far n as far srn MN/sw WI.

Main fcst concerns in the short term focus on how far n pcpn
associated with the srn branch disturbance wl move late tngt/Thu.

Tngt...The srn branch closed lo is progged to move slowly to the ne,
reaching ern Kansas/wrn Missouri by 12Z Thu while the nrn branch
shrtwv/accompanyin dpva lift ne toward the border of Manitoba/far nw
Ontario. While most of the Upr Lks wl remain under an axis of drier
lo/mid lvl air and larger scale h85-5 qvector dvgc btwn these
disturbances, some hier h85-5 rh on the nrn fringes of the mstr
shield ahead of the srn branch disturbance is fcst to impact the
scentral cwa. But since the dry llvl feed of air out of the slowing
departing Hudson Bay hi pres is fcst to persist, the bulk of the
hier res models show pcpn in the form of sn reaching just s of the
city of Menominee by 12Z Thu. Wl retain some lo chc pops only over
far srn Menominee County toward 12Z. Otrw, the combination of
thickening hi/mid clds and a steady e wind wl limit the diurnal temp

Thu...The short term guidance shows the closed lo moving to near St
Louis by 00Z Fri, with hier mid lvl mstr influencing the se 1/3 or
so of the cwa on the nrn fringes of area of upr dvgc in rrq of h3
jet max within the confluence zone of the separate branch flows. The
rest of the cwa wl remain under the axis of deep lyr qvector dvgc
btwn the larger scale srn branch forcing influencing WI/Lower MI and
the nrn branch disturbance tracking toward Hudson Bay and remain
dry. Expect a sharp gradient of pops over the scentral, where an
upslope e wind may at least minimize the influence of the llvl
drying associated with the slowly departing Hudson Bay hi pres, as
indicated by the 12Z NAM model. Given the pattern featuring a Hudson
Bay hi pres that favors dry wx for Upr MI, tended toward the drier
scenrios for pops fcst. Although the fcst thermal profiles indicate
this pcpn wl fall mainly as sn, the incrsg late March sun angle that
allows sfc temps to rise at least a couple degrees above 32 wl limit
sn accum potential.

.LONG TERM...(Thursday through Tuesday)
Issued at 456 AM EDT WED MAR 29 2017

Medium range model guidance continues to indicate that split flow
will dominate for the next 7 days with the southern stream very
active. Pcpn that occurs over the Upper Lakes will largely depend on
whether any of the active southern stream systems track far enough n
to affect the area as weaker northern stream energy tracking mostly
thru southern Canada won`t produce any pcpn of note for the Upper
Lakes. The first southern stream system of interest is currently
moving out of NM into w TX. As this energy lifts ene, ejected by the
next shortwave trof dropping into the sw CONUS, some pcpn will
likely brush portions of Upper MI Thu/Thu night. As the new sw
energy moves out over the southern Plains/Lower Mississippi Valley
early next week, weaker northern stream energy will pass over or
near the area with little risk of pcpn. Heading into the middle of
next week, attention will turn to the next shortwave trof that
reaches the southern Rockies on Mon. This energy may lead to
unsettled weather here in the midweek period, which could include
wintry pcpn. As for temps, split flow will keep any really cold air
from plunging s thru Canada into the Great Lakes, resulting in temps
overall above normal thru this fcst period. Looking farther ahead,
CPC and NAEFS 8-14day outlooks valid Apr 5-11 suggest a continuation
of above normal temps.

Beginning Thu/Thu night...mid-level low lifting thru the southern
Plains today will reach the Lower Ohio Valley by Fri morning. While
quite far s, additional weak energy lifting farther n from this low
should help push isentropic ascent far enough n to spread at least
some light pcpn into southern portions of Upper MI Thu/Thu night.
However, high pres currently over Hudson Bay will be over Quebec on
Thu, providing a feed of drier air from the e which may work to hold
off pcpn. Since the high is displaced well to the ne, believe the
persistent isentropic ascent will overcome the dry air at least over
s central Upper MI and e along Lake MI. Fcst soundings support ptype
as snow. Given light intensity of snowfall and temps generally above
freezing, any snow accumulations will be light, probably not more
than around 1 inch. A few models indicate pcpn amounts upwards of
around 1/3rd of an inch in Menominee County. Seems high given the
weak forcing, but will be something to monitor in later model runs.
Elsewhere, expect mostly cloudy skies. With thinner cloud cover w,
temps may still top out well into the 40s over far western Upper MI
on Thu while the -sn is occurring over the s central.

Fri/Sat...a couple of northern stream shortwaves will track across
northern Ontario and the Upper Lakes. With first shortwave on Fri
passing well to the n of here, not expecing any pcpn. In the wake of
that shortwave, sfc high pres ridge will build into the western
Great Lakes for Sat even though second shortwave approaches. Weak
forcing suggests very little risk of pcpn on Sat either, so fcst
will reflect dry weather Fri and Sat. Steady n to ne wind on Fri
will lead to a cool day, especially near Lake Superior. Increasing
sunshine from the w will allow temps to rise into the 40s in the
interior w half. Will still be cool near Lake Superior on Sat but
with lighter gradient winds across the lake, temps will be higher
than Fri. Well inland, temps should reach 50F or higher.

Another northern stream shortwave will reach northern Ontario late
Sun. Better forcing and waa/isentropic ascent will pass n of here,
so again not expecting any pcpn. With winds veering around to a
southerly direction, it will be warmer near Lake Superior on Sun.
Warmest conditions will be over the w where temps should reach the
mid 50s.

Mon thru southern stream shortwave should pass well s and
se of here Mon/Tue with attention turning to the next one that will
be over the southern Rockies. This system may interact with the next
upstream shortwave that will track farther e into N America before
dropping se (rather than dropping into the sw CONUS per previous
waves), a result of an amplifying trof developing over the ne
Pacific. The 00z ECMWF has backed off on interaction that led to a
potentially significant snow for portions of Upper MI on Tue as
shown by the 12z run. However, 00z CMC ensembles show a few more
members than the 12z run supporting a potentially wrapped up Great
Lakes storm system midweek. Will be something to monitor in the
coming days, but for now, nothing supports more than some chc pops
in this period with ptype mainly rain.

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 125 PM EDT WED MAR 29 2017

This fcst period wl be dominated by a good deal of hi clds that wl
tend to thicken with time at SAW. Since the disturbance responsible
for this hi cld wl remain well to the s of Upr MI and dry llvl
air associated with Hudson Bay hi pres wl prevail, pcpn and lower
vsbys/cigs wl remain to the s of the TAF sites as well. So VFR
conditions wl be the rule.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 247 PM EDT WED MAR 29 2017

Ene winds up to 20 to 25 kts will be possible tonight into Fri under
the sharper pres gradient between slowly deparing Hudson Bay hi pres
and a slow moving lo pres that will be drifting from the southern
Plains toward the Lower Great Lakes. Winds for later Fri thru Mon
will be under 20 kts as a weaker pres gradient becomes established
across the western Great Lakes.

Upper Michigan...
Lake Superior...
Lake Michigan...


LONG TERM...Rolfson
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