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Area forecast discussion 
National Weather Service Marquette Michigan
739 am EDT Tuesday Sep 1 2015

Short term...(today and tonight)
issued at 414 am EDT Tuesday Sep 1 2015

Much of the focus on the short term will be with the weak surface
trough decaying as it moves east across the area today and tonight
and the potential for a few showers/thunderstorms along it. Water
vapor imagery and rap analysis show the upper ridge axis is shifting
east across Lake Huron early this morning...which is allowing a
plume of moisture stretching from northwest Mexico to James Bay to
slowly move east towards the area. Did see a few showers along the
surface trough and moisture plume earlier in the night in northern
Minnesota but they have since dissipated. Out ahead of the
trough...the combination of very radiational cooling and
southwesterly winds pulling moist air across Lake Michigan has
produced fog once again over eastern Upper Michigan. The lowest
visibilities have been right along the Lake Michigan
shoreline...with visibilities at 1/4mi at times. Did issue a marine
dense fog advisory earlier in the night based off the satellite
coverage of the fog on Lake Michigan and the visibility rapidly
falling once it reached kisq. The rest of the area has seen mostly
clear skies and areas where the winds have decoupled have seen
patchy ground fog. Expect that to continue into the first part of
the morning hours before lifting to a brief stratus deck and then
dissipating. On final item to note for this morning is the scattered
borderline MVFR/VFR clouds in western Wisconsin. These have been
shifting to the north this morning and will aid some diurnal clouds
over portions of the area today.

Precipitation potential is a little more up in the air for today and
largely tied to several features coming together in a narrow
corridor this afternoon. First...the moisture plume to the west of
the area on water vapor will shift to the east and across the
west/central County Warning Area this afternoon. While it looks fairly impressive on
WV appears that the models are doing fairly well on the
very thin pockets of moisture within that area. Second...some of the
models have hints of a weak shortwave in eastern South Dakota that
will lift to the northeast and only brush the west/central u.P. This
afternoon. While most of it will stay northwest of the land
County Warning Area...there are some hints at a southern appendage to the shortwave
that may work with the surface trough and pockets of moisture around
850mb to develop some showers/thunderstorms this afternoon. Coarse
models are showing limited development...while the higher resolution
models (including 14km ecmwf) are showing some isolated shower
development between 19-22z over west-central Upper Michigan
(generally from kiwd through Baraga County and into northern
Marquette county). Ncar WRF ensembles focus on that area too for
initial development but then expand it east-southeast into the
central u.P. This evening (marquette/Alger/Delta and northern menominee).
Have kept the probability of precipitation confined to the area immediately ahead of the
weak trough and over the land areas of west/central Upper Michigan.
Will continue to show slight chances based off the uncertainty of
the shortwave being close/strong enough to help the showers and also
the marginal moisture...although did include a few chances for the
southern Houghton and Baraga County area due to the consistency in
the models on something occurring in that area. In addition...there
are indications of a very narrow corridor of stronger 0-6km bulk
shear (30-35kts) over north central Upper Michigan although most
areas will be in the 20-25kt range. Combining that with MLCAPE
values of 1-2k j/kg this afternoon...there is the potential for a
stronger storm if all of the pieces come together.

The trough will continue southeast and weaken through the night
tonight...leading to a subtle wind shift to the west-northwest.
Showers should dissipate through the evening hours over the
northeastern part of the County Warning Area and lead to a partly cloudy to mostly
clear night. Will have to watch for fog development again
tonight...although the models are showing slightly drier low level
air. Have included patchy to areas of fog for now and a lot will
depend on the drying behind the weak trough.

Long term...(wednesday through monday)
issued at 519 am EDT Tuesday Sep 1 2015

Upper level ridge to start on Wednesday from southwest Continental U.S. To the
northeast Continental U.S. Allows for possible afternoon/evening rain showers/thunderstorms and rain Wednesday and
Thursday. Expect the ridge to build back from Southern Plains to the upper
Great Lakes/northern Ontario by late this week in response to strong
upper trough digging from western Canada down the western Continental U.S. Coast.
Trough will continue digging south...possibly as far as California
by this weekend while ridge expands over rest of Great Lakes and
northeast Continental U.S.. at the surface...slow moving cold front will be stuck
over the plains in between the upper trough and upper ridge. Since
upper pattern changes little this weekend and front will be parallel
to flow aloft...front will struggle eastward Saturday into Sunday.

Shortwave currently over Colorado/neb/KS intersection is forecast to lift
northeast to upper Mississippi River valley by 12z Wednesday and then to
move over WI/Upper Michigan Wednesday afternoon into Wednesday night. MLCAPES focused
more from Dakotas/northern Minnesota east-southeast across WI and lower Michigan. Mean
layer winds prefer the European model (ecmwf)/NAM/Gem-regional showing
majority of quantitative precipitation forecast over northern WI with the shra/tsra. Also northerly
gradient/lake breeze enhanced winds off Lake Superior will stabilize
low-levels closer to Lake Superior and over eastern County Warning Area. Chance probability of precipitation
highest toward WI border. For temperatures...stuck toward previous forecast
with middle 80s inland west half. Cooler middle-upper 70s near Lake Superior
with onshore winds. If those onshore winds start up quicker...could
see readings ending up cooler than forecast currently shows. Kept
lingering probability of precipitation mainly scntrl on Wednesday night as the shortwave drifts
across and since scntrl will be on northern edge of 850 mb convergence
zone and in a potential middle-level fgen area with the shortwave.

Subsidence increases in wake of shortwave later Thursday into for most part think it will be mainly dry couple days.
Winds turn back to south-southeast-S which results in better chance of warming
for all areas away from Lake Michigan. 850 mb temperatures bump up a couple
degrees as well by so after low-middle 80s on Thursday...should see at least
upper 80s for West County warning area on Friday afternoon. Low-middle 80s elsewhere...expect
upper 70s near Lake Michigan. No change at all the humid conditions that
really start up today...with dewpoints solidly in the 60s. Though not
in the forecast the entire time...cannot rule out fog just about
anytime Wednesday through Friday especially near the Great Lakes
shores where there is some onshore wind component. Have seen this
last few days and no reason to believe it will not continue in at
least some shape or form.

Into this weekend. Eventually...stronger shortwave trough forecast
to move into western Canada will act as kicker to the trough over
the northwest Continental U.S. And push the cold front to the east while
developing a surface low on its northern edge at the forefront of the
initial upper level trough. Entire system moves across upper Great
Lakes Sunday into Monday. European model (ecmwf) in 3 of its runs over last few days
has hinted that rain showers/thunderstorms and rain may break out well ahead of main front
downstream of surge of 2000 j/kg MUCAPE from northern plains to
northwest Ontario either Saturday or Sunday. 850-300mb thickness
lines would support that potential showing northwest-southeast flow Saturday and west-
east flow on Sunday. Latest European model (ecmwf) now builds upper ridge more and has
850 mb Theta-E ridge as far north as southern Manitoba and northwest
Ontario Friday night into Saturday. If this occurrs it would likely
stay dry over Upper Michigan Friday night into Saturday as shortwaves
and associated rain showers/thunderstorms and rain would stay well to the northwest of Upper
Michigan/Lake Superior. Then...once the shortwave trough over the
northwest Continental U.S. Moves eastward...there would be increasing chances
of rain showers/thunderstorms and rain as the weekend concludes and on into Labor Day. Kept
probability of precipitation at slight chance over south and east Friday night into Saturday
night with chance probability of precipitation over far northwest County Warning Area. By Sunday...brought chance
probability of precipitation over more of the North County warning area but still kept probability of precipitation slight chance at
best over scntrl farther away from the Theta-E ridge and more into the
larger scale ridge.

GFS blows cold front through quickly Sunday night into Monday while
European model (ecmwf) is slower mainly due to showing more of a cutoff upper low
over the western Continental U.S. Saturday night into Sunday. Will continue to
use consensus probability of precipitation for forecast which are highest for Sun night into
Labor Day. Still looks cooler for Sunday and Labor least
compared to warmth this week. Based on trends from latest models...
confidence is lessening in a significant cool down next week. Stay

Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 739 am EDT Tuesday Sep 1 2015

Fog will be the primary concern for the taf period...both at the
beginning of the period and overnight tonight. Have started both
kcmx/ksaw out at vlifr and expect to quickly diminish over the next
couple of hours. Then a weak surface trough will moves across the
area through the day today and could lead to a few showers. Have
just addressed the showers with vcsh at kiwd/kcmx for this morning
based off the returns seen on kdlh radar. As daytime heating is
maximized...could see additional showers and maybe a few
thunderstorms develop but most will be between the three taf sites.
If they affected a site...think kiwd or ksaw would be the most
likely. Finally...although there will be some drying of the lower
levels...think ground fog will develop again tonight and have put
in visibilities falling to MVFR values for now.

Marine...(for the 4 am Lake Superior forecast issuance)
issued at 414 am EDT Tuesday Sep 1 2015

Southwesterly winds will weaken through the day today as a weak
surface trough slowly drops southeast across Lake Superior today
and tonight. This will lead to winds falling below 15kts this
afternoon and remain that way into Thursday as a high pressure
ridge noses back northwest into the upper Great Lakes region.
Southerly flow will strengthen Friday into the weekend ahead of a
broad low pressure trough stretching from central Canada to the
Central Plains that will move east into the upper Mississippi
Valley. Finally...expect patchy to areas of fog to occur over Lake
Superior into Thursday.

MQT watches/warnings/advisories...
Upper Michigan...
Lake Superior...
Lake Michigan...
dense fog advisory until noon EDT today for lmz248-250.



Short term...srf
long term...jla

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