Area Forecast Discussion
Issued by NWS Marquette, MI
FXUS63 KMQT 210832
Area Forecast Discussion
National Weather Service Marquette MI
432 AM EDT WED SEP 21 2016
.SHORT TERM...(This evening through Wednesday)
Issued at 414 PM EDT TUE SEP 20 2016
WV imagery and RAP analysis indicated a zonal pattern across most of
the nrn CONUS with a trough moving into the Pacific Northwest. A
weak shortwave trough and area of 800-600 mb fgen supported some
light showers or sprinkles from near KDLH into wrn Upper Michigan.
Very dry air below 700 mb will limit the extent of the pcpn with only
slight chance pops mentioned late this afternoon. Otherwise, mid
clouds were thickening over the area with a broad area of 300-310k
isentropic lift in advance of sfc low pres over South Dakota.
Tonight, expect mid clouds to linger over the region in the waa
pattern with the 850-700 baroclinic zone lingering over the area.
Shra/tsra are expected to remain south of the cwa, closer to the
850mb front and higher MUCAPE values. Otherwise, the clouds will
keep min temps mainly in the 50s.
Wednesday, pcpn chances will increase from s to n as the 850 mb
front gradually lifts to the north. Additional weak shortwaves in
the fast zonal pattern will likely also support shra/tsra
development. However, with the relatively dry low level ne flow
north of the front, the pcpn into the nrn cwa will be slow with
likely pops south and only chance pops north. With MUCAPE values
fcst into the 500-1000 J/Kg over the far south some TS will also be
possible. The thickening clouds will limit highs to the upper 60s to
.LONG TERM...(Thursday through Tuesday)
Issued at 432 AM EDT WED SEP 21 2016
An increasingly amplified pattern is still on track to develop
across N America for the remainder of this week into the weekend.
Ridge/positive height anomaly currently moving into nw Canada will
strengthen as it shifts across the Northwest Territories to Nunavut
by the end of the week. The magnitude of the positive height anomaly
at 500mb will reach 3 standard deviations above the long term late
Sept avg. To the s of this anomaly, a trof will amplify over the
western CONUS over the next few days, and the building downstream
ridge over the central CONUS will then link up with the n central
Canada positive height anomaly, leading to a sharp mid continent
ridge for a brief time. In response, trof over se Canada will deepen
and expand into the ne CONUS this weekend. This suggests that after
wet weather into Thu, a drier period should mostly dominate Fri/Sat
and potentially thru Sun as sfc high pres associated with the sharp
upstream ridge builds se into northern Ontario and the Upper Great
Lakes. Early next week, a more progressive flow regime should begin
to take shape again. Initially, building of a ridge into western N
America will send a shortwave se into the Upper Lakes later Mon/Tue.
This wave will incorporate at least some of the energy in the
western CONUS trof with the remainder dropping s. A period of shra
will accompany this shortwave across the area at some point Sun/Mon
with drying following for Tue. As for temps, readings will probably
not stray far from late Sept normals during this period.
Beginning Thu, last in a string of weak shortwave energy lifting ne
thru the western Great Lakes will move e of the area by late aftn.
Meanwhile, downstream of the western Canada ridge, a stronger
shortwave will drop into northern Ontario during the day and then
into Quebec Thu night. Following this wave, sfc high pres associated
with the sharpening mid/upper ridge in central Canada will build se
into northern Ontario Thu night, pushing frontal boundary extending
from the Plains to the Great Lakes southward. As a result, expect a
trend for shra Thu morning to diminish and/or end from nw to se
during the aftn thru Thu night.
With sfc high pres dominating northern Ontario on Fri and frontal
boundary/baroclinic zone shifted farther s and sw, expect a dry day.
Will need to watch development of pcpn into the northern plains
where strengthening southerly flow/isentropic ascent ahead of
western CONUS trof leads to an expanding pcpn area. Right entrance
upper divergence with a reoriented upper jet in a nw-se direction
across northern Ontario to New England could aid the expansion of
pcpn toward Upper MI late Fri or Fri night.
ECMWF has been most insistent on pcpn briefly streaking se into at
least western Upper MI Fri night into Sat underneath right entrance
of upper jet and within an eastward extension of isentropic ascent
from the northern Plains. GFS/CMC have been more varied on whether
or not the pcpn will reach the area, but since majority of GFS/CMC
ensembles support the streak of pcpn, fcst will reflect chc pops
spreading into the far w Fri night and expanding e into central
Upper MI Sat morning before pcpn area dissipates.
Fcst for Sun thru Tue is highly uncertain, much more than is
typically the case at this time range and no different from the last
few days. Over the last 4 days, medium range guidance has shown
considerable spread in what happens with the western CONUS trof and
how the flow evolves across southern Canada this weekend thru early
next week. The 00z GFS is back to showing a mid level low closing
off over the Upper Mississippi Valley/western Great Lakes early next
week, a solution that appeared once days ago though it got to that
solution in a different manner. At this point, consensus of recent
days guidance is for a shortwave which incorporates at least some of
the energy in the western CONUS trof to reach the area early next
week, but wouldn`t be surprised at all if something completely
different occurs. Maintaining some continuity with previous fcst,
will show chc pops spreading slowly e across the area Sun/Sun night,
lingering Mon then trending dry on Tue.
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 153 AM EDT WED SEP 21 2016
Although there wl be a good deal of mid clds at times and perhaps a
few -shra especially this aftn, dry llvl air wl ensure VFR conditions
prevail at all 3 TAF sites this fcst period. Thicker clds and more
numerous showers will arrive by this evng. While lingering near sfc
dry air wl likely maintain VFR conditions even if some showers
occur, MVFR conditions wl probably dvlp after 22/06Z.
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 414 PM EDT TUE SEP 20 2016
West southwest winds to 25 knots will diminish to 20 knots or less
tonight into Wed as the pres gradient weakens with the Canadian low
lifting farther ne across Hudson Bay. Winds will remain blo 20 kts
into Saturday under a weak pres gradient across the Upper Lakes.
Southerly winds will increase Sunday to 20 knots as a low pressure
trough approaches from the west.