Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Marquette Michigan
409 am EDT Tuesday Jul 29 2014

Short term...(today and tonight)
issued at 402 am EDT Tuesday Jul 29 2014

Upper trough centered near James Bay slowly drifts westward through
tonight. Weak surface trough is currently crossing northern Upper Michigan
while another front...pretty weak as still to north of Lake
Superior. Passage of the second front tonight should allow for more
ridging at the surface to develop by late tonight. Hard to time shortwaves
along with pockets of deeper moisture and increased instability will
drive the shower/thunder chances over Upper Michigan into tonight.
Following persistence and trends from last couple days...expect
maximum of coverage to rain showers and thunderstorms and rain to occur where these features
sync up with peak heating of the day. National Weather Service radar loop from the upper
Great Lakes region...thankfully including MQT radar again...along
with radar imagery from Environment Canada indicates relative minimum
in rain showers/thunderstorms and rain at this time over Upper Michigan. Area of enhanced showers within
ribbon of higher 700 mb-500 mb relative humidity and elevated MUCAPE up to 300 j/kg is
dropping southward across portions of northwest Ontario and the
Minnesota arrowhead.

Majority of short term models in good agreement that the area of
deeper moisture and shortwave/associated 700 mb-500 mb q-vector convergence
to northwest of Lake Superior this morning crosses the area later this
morning into middle afternoon. By late afternoon...axis of higher relative humidity and MLCAPE
up to 500j/kg will be more oriented from western Upper Michigan to
scntrl Upper Michigan. Meanwhile...expect a minimum in forcing and
moisture and MLCAPES from Isle Royale to eastern Upper Michigan. Showed
highest probability of precipitation over the interior west and central late morning into
middle afternoon. After the isolated rain showers around through daybreak depart over
the east County Warning deeper moisture and direct impact from the
incoming shortwave results in little if any additional chances of
rain today. Similar high temperatures to ydy...with 60s near Lake Superior
and into the lower 70s over the scntrl.

Cape during peak heating of the day continues to appear more skinny
with normalized cape values less than 0.1. Effective shear may try
to reach 30-35 kts this afternoon...but overall setup of more clouds and
less realized instability supports stronger storms staying farther
south and west of County Warning Area where MLCAPES are more toward 1000j/kg this
afternoon. Even so...cannot count out an isolated strong storm over the west
half of the County Warning Area early to middle afternoon...especially away from the Keweenaw.
Mean storm motion/700 mb winds are oriented northwest to southeast but more organized
or stronger storms would move more north to south...similar to isolated
storm that occurred earlier tonight over northwest WI just to west
of kiwd.

Models agree that ribbon of deeper moisture drops south of the area
tonight while generally there is subsidence/q-vector divergence over
Upper Michigan. Showers and thunderstorms from late this afternoon should fade
away quickly this evening near WI border with negative dynamics and
loss of daytime heating. Another batch of middle-level moisture and
uvm currently just to west of James Bay is forecast to stay mainly
to the east of Lake other than increasing middle clouds
later tonight as this drops south...did not carry any additional
chances of shra/tsra. Could see fog overnight as ridging and light
winds take hold...especially over the west half where rain is more
likely today.

Long term...(wednesday through monday)
issued at 334 am EDT Tuesday Jul 29 2014

The upper level low centered near James Bay will persist through
the rest of the work week...before gradually weakening and lifting
northeast this weekend and into early next week. With a ridge over
the western conus/Canada...expect the flow aloft to be out of the
northwesterly direction through the long term period and lead to
temperatures being a little below normal. 850mb temperatures will be the
coolest on Wednesday...around 8c...before rising to around 12c on
Thursday and remaining into the weekend. Thus...expect Wednesday to
have the coolest highs of the work week (in the upper 60s and lower
70s). While highs will be a few degrees below normal on Wednesday
expect a gradual trend to near normal temperatures by Friday and
continue into the weekend.

As for precipitation...expect generally diurnal showers over
interior locations for Wednesday through Friday...although the
several shortwaves rotating around the upper low could lead to a
couple periods of showers during the overnight hours. On
Wednesday...think coverage will be fairly limited (and over the
south central or maybe east) as the main shortwave energy brushes
the northeast half of the County Warning Area. Deep moisture appears to be the
main limiting factor but there is a pocket of moisture that
rotates through during the day between 800-700mb. Thus...will keep
probability of precipitation in the slight or low chance category for mainly the central
and east away from the stability of Lake Superior. There are hints
of a weak shortwave producing a few showers on Wednesday
night...but confidence is too low in include anything more than
slight chance of showers. Thursday should be similar to
Wednesday...but with a little better focus over the south central
due to the potential of a stronger lake breeze off Lake Michigan.
Will have the highest probability of precipitation on Friday (high end chances) models
continue to indicate a stronger upper trough rotating through during
the day. It appears subsidence behind Friday/S trough should lead to
a dry Saturday. Thus...have continue the downward trend in probability of precipitation.
Precipitation chances will increase on Sunday afternoon/night as another
shortwave drops southeast across the area. This wave may provide
some reamplification of the upper trough and continue precipitation
chances into Monday.

Finally...for thunder potential...MLCAPE values are below 500 j/kg
on Wednesday afternoon and will cap at slight chances.
Thursday/Friday have MLCAPE values a touch higher over the south will have chances there and slight elsewhere where
there are probability of precipitation in the afternoon. Friday will also be helped by the
shortwave...but with 0-6km shear values still weak (15-20kts) not
expecting anything more than brief heavy rain and some small hail in
any of the stronger storms.

Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 140 am EDT Tuesday Jul 29 2014

Expect scattered-broken showers to impact mainly iwd and cmx this morning in
advance of an upper disturance and under axis of somewhat moister/
more unstable air. Although VFR conditions will predominate...lower
visibilities are possible under some of the heavier showers. Since rain has
fallen at iwd and cmx...some fog may lower visibilities there toward
sunrise if there is enough clearing at those sites. Another round of
showers and some ts will impact the sites later today with the aprch
of another disturbance in the presence of daytime heating. There is
too much uncertainty on timing/placement of ts to include an
explicit mention of ts at this time. Best shot at kcmx would be middle morning
to early afternoon...while it would be slightly later at kiwd. Although
MVFR and even IFR conditions are possible under some of the heavier
showers...VFR conditions will predominate. Drying/subsidence in the
wake of this disturbance will end the shower threat late in the

Marine...(for the 4 am Lake Superior forecast issuance)
issued at 402 am EDT Tuesday Jul 29 2014

With a weak pressure gradient typical of Summer dominating this
forecast period...expect winds under 20 kts through the week.

MQT watches/warnings/advisories...
Upper Michigan...
Lake Superior...
Lake Michigan...


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

National Weather Service Glossary of Abbreviations