UPDATED 11:20AM
The latest SPC update kept Lee/Whiteside county in the slight risk area. A partial portion of southeast Lee county is in the enhanced risk as well.
RISKS
Best Chance: Severe Winds (50MPH+)
Decent Chance: Hail up to golf ball size
Lower Chance: Tornado
–All Modes of Severe ARE Possible–
Timing
After 3PM to 11PM
Storm Movement
ENE 50-60kts(57.5-69.0MPH)
Safety
You will have very little time to react to a warned storm. Be sure to have a way to receive warnings, and remember… tornado sirens are only effective while you are outside.
DETAILED FORECAST
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So we’ve been monitoring forecast models and constant hourly updates on the HRRR and the 6 hour update on the NAM runs. We run into a scenario where HRRR forecast models bring out extreme scenarios of discrete/scattered cell development across our area and much of Illinois, while the NAM keeps us dry until a large linear storm system rushes through the area. At this point in time, I believe a scenario of both will occur, but not to the extreme of the HRRR models.
One thing that has been consistent is storm movement, and the required atmospheric conditions for storm development.
We sit along the enhanced outlook area which means we are still in a decent area for seeing severe weather. Assuming the development of discrete cells happen ahead of the cold front, all modes of severe weather are possible at this point. The main threat would be large hail and heavy rain with these discrete cells. Tornado development (or continuation) won’t be ruled out as our wind shear is showing capabilities of tornado profiles. However, due to other atmospheric conditions, our tornado threat won’t be as high as those in central and southern Illinois. Again, in the discrete cells hail will be the largest threat.
With the second round of storms, I foresee this happening as the cold front moves inward. Regardless of discrete cells or not, the likelyhood of a linear storm system progressing through the area is a very high chance. This will bring in a high wind risk for the area mainly 45MPH or higher will be possible. Small hail won’t be ruled out either. Tornado threat can’t be ruled out, as we know tornadoes can happen in linear systems as well, but it won’t be as high as with the discrete cell threat.
I mentioned that storm movement has been consistent. This has held true for every model. The storms are expected to move ENE at a very fast pace likely of 50-60kts (57.5-69MPH). This will leave very little time to react to any warnings especially on developing storms. Be sure to have a way to receive warnings, and remember.. tornado sirens are only effective while you are outside.
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-Tim
PREVIOUS UPDATE:
Our chances for severe thunderstorms are on the rise for later this afternoon into this evening. An area of low pressure will track nearly directly overhead by this evening bringing unusual warmth and moisture for this time of year into the area. The combination of these dynamics will produce scattered strong to severe thunderstorms after 3pm this afternoon.
Winds aloft will remain favorable for all hazards of severe weather including tornadoes, large hail and damaging winds.
These storms will also be moving very quickly leaving little time to take action should a warning be issued.
We encourage you to stay weather aware through the afternoon and early evening hours as this threat continues to evolve. Our update frequency will be enhanced today as we monitor the situation. Make sure you have a way to receive warnings and seek appropriate shelter should a warning be issued for your area and action is necessary.
-Andrew
