Threats Assessment Discussion

FXUS21 KWNC 211845
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT June 21 2019
SYNOPSIS: An upper-level ridge over the central U.S. is forecast to dominate 
the weather pattern during week-2. This is likely to result in 
warmer-than-normal temperatures and high humidity over much of the central US. 
This combination may lead to excessive heat, especially over the Corn Belt 
region and Upper Mississippi Valley through the first half of the week. The 
southeastern U.S. is also predicted to be unsettled as a trough sets up over 
the Gulf of Mexico during week-2, leading to a slight risk for hazardous 
rainfall in and around Louisiana.
Slight risk of excessive heat for portions of the Northern Plains and Upper 
Mississippi Valley, Sat-Tue, Jun 29-Jul 2.
Slight risk of heavy precipitation over Louisiana and its immediate vicinity, 
Sat-Fri, Jun 29-Jul 5.
FOR SATURDAY JUNE 29 - FRIDAY JULY 05: An upper-level ridge over the central 
CONUS is forecast to persist during the entire week-2 forecast period. Daily 
maximum temperatures are projected to be in the lower-90s over the northern 
Plains and mid-80s over most of the upper Mississippi Valley. Lower humidity 
values over the Plains will allow warmer temperatures than over the Mississippi 
Valley. However, heat index values, which account for both temperature and 
humidity, are likely to be highest over the northeastern Plains and Upper 
Mississippi Valley since dew points may reach 80 degrees. Earlier this week 
model guidance had suggested that the excessive heat would last through the 4th 
of July, but the latest several GEFS and ECMWF ensemble runs predict the core 
of the heat to end earlier. Therefore, our slight risk hazard for excessive 
heat over this region extends from June 29 to July 2. 
Some sporadic episodes of convective precipitation will be possible throughout 
week-2 over parts of the northern tier of the CONUS, but the lack of 
organization and uncertainty in regards to their exact placement precludes us 
from posting a hazard. The GEFS and ECMWF ensemble have consistently hinted at 
organized heavy rainfall centered on Louisiana during week-2 that could exceed 
1 inch per day. It's too early to pinpoint exactly which days Louisiana will 
experience hazardous levels of rainfall, so we have a posted a slight risk 
hazard for all of week-2 indicating that there is a slight risk of hazardous 
rainfall on any given day.
Model guidance continues to show very warm temperatures for parts of mainland 
Alaska during week-2 associated with strong ridging in place. The warmest 
temperatures are likely to be over southern and western Alaska, and may reach 
15-20 degrees above their climatological average values.
FORECASTER: Kyle MacRitchie