Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

FXUS63 KGRR 200048

Area Forecast Discussion
National Weather Service Grand Rapids MI
848 PM EDT Fri Jul 19 2019

Mesoscale Discussion

Issued at 848 PM EDT Fri Jul 19 2019

Convection continues along a convergent boundary from Kalamazoo
toward Detroit, though has only thus far presented a heavy
rain/lightning threat thanks to marginal shear. A low-end flooding
threat may materialize over southern Jackson county over the next
hour or so given antecedent conditions (e.g. heavy rain earlier 
in the week from the remnants of Barry). Otherwise, we're not 
overly concerned about that activity at the moment. 

Our attention is turning toward the developing MCS across central
Wisconsin. The environment ahead of the system is more than
conducive for continued maintenance with the only real question 
of where the core of the system--and hence severe weather threat--
will go. As a stationary supercell becomes ingested to the 
northern end of the developing line, we expect a large bow to 
emerge with an acceleration of storm motion over the next few 
hours. By that point in time, an easterly track is preferred given
a plethora of "traditional" measures, such as strong capping 
across central Wisconsin eastward (e.g. 700 mb temps pushing 15 C)
and westerly 500 mb flow. With this in mind, it appears the 
southern edge of the system will brush US-10. However seemingly 
unlikely, we would be remiss to ignore the possibility the system 
continues southeast and impacts a larger portion of our area. But 
again, the main threat zone appears to be US-10. Based on the 
current storm motion with an anticipated increase in speed, the 
threat appears to be from midnight (shoreline) to 5AM (central 
Lower Michigan), give or take an hour.

Given the storm mode, damaging winds are the main concern. Should 
the storms indeed turn into a bow, the winds could be fairly 
serious at the apex. We'll also have to keep an eye on the heavy 
rain threat (assuming an easterly motion) with perhaps a several 
hour period of training thunderstorms in an environment with 2"+ 

The bottom line is that areas along/north of US-10 are at greatest
risk for damaging winds between the hours of 12 - 5 AM, with a 
lesser threat for localized flooding. 


Issued at 328 PM EDT Fri Jul 19 2019

- Severe threat across Southeast Lower Michigan this afternoon and
  across Northern Lower Michigan tonight

- Severe threat across Central Lower Michigan on Saturday


.DISCUSSION...(This evening through next Friday)
Issued at 328 PM EDT Fri Jul 19 2019

The threat for strong to severe storms across our southeast 
zones, where greater than 5000 j/kg of sfc based CAPE currently 
exists, will continue into early evening, then subside with loss 
of diurnal heating. 

Heights are rising overnight as an upper ridge axis builds into
Lower Michigan and warm mid level temperatures are expected to
cap strong convection through Saturday morning. The synoptic
pattern tonight would indicate that any MCS moving out of northern 
Wisconsin will track eastward and stay north of our northern
zones. Some of the CAMS turn the derecho in Wisconsin southeast 
into our area. We will have to watch how this evolves.

A better indication for severe weather is on Saturday afternoon
and evening as heights fall and a cold front pushes south into the
very unstable and most air. This threat will continue through 
Saturday night.

Rain and embedded thunder is expected Sunday as a sfc wave tracks
along the front then much cooler and drier for Monday and the rest
of the week.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 753 PM EDT Fri Jul 19 2019

VFR conditions will prevail this evening with the exception of
isolated IFR in heavy downpours from BTl to JXN early this
evening. There is still uncertainty whether a line of severe
thunderstorms currently in Wisconsin will make it into central
Lower Michigan. The greatest chance of that will be from MKG to
GRR after 04Z. 

Southwest winds around 10 knots overnight will continue through
tomorrow afternoon and will gust to 20 knots at times.
Thunderstorms may be arriving before 00Z Saturday especially
from MKG to GRR and LAN but were not included in this forecast.


Issued at 328 PM EDT Fri Jul 19 2019

No change to the Small Craft Advisory. Winds and waves will
subside this evening. There is a low chance for strong to severe
thunderstorm winds north of Pentwater by midnight. Areas of fog
are expected as winds decrease later tonight.


MI...Excessive Heat Warning until 8 PM EDT Saturday for MIZ056>059-

     Heat Advisory until 8 PM EDT Saturday for MIZ037>040-043>046-



National Weather Service Glossary of Abbreviations