Issued: 12am on Thursday, January 1st 1970
Technical Forecast Discussion
Short Term (Sunday 9/29 through Wednesday 10/2)
Strong upper-level troughing over the Pacific NW with distinct mid-level ridging for the SE United States has generated this amplified flow pattern across the country. Throughout this short term, this highly influenced Jet will continually be squeezed SW’ly to NE’ly through the ‘Four Corner States’ and upper Midwest with relatively strong flow aloft (up to 130-150knots). A well-organized surface low ~998mb emerged from the Jet’s left exit region earlier on Sunday, which is currently located over eastern Wyoming. Future progression northeasterly through the upper Midwest is imminent over Sunday night and into Monday morning as its warm front widely extends eastward across the lower Great Lakes. This ridge influence and surface high pressure (~1023mb) just south of the region (located over western North Carolina) will remain in control Monday through Wednesday and offer mostly dry, but exceptionally warm and humid conditions. Dewpoints will consistently linger in the upper 60s with high temperatures climbing well near 90… As of Sunday evening, the mentioned warm frontal boundary is situated along south-central Ohio. Weak diurnally driven precipitation has developed near the boundary itself as southern Ohio remains fairly unstable. Nearing sunset, Cape values still remain around 1000 J/kg with outflows extending SW’ly of this precipitation. Additionally, current Hi-Res models are in agreeance of some isolated thunderstorm development through the late Sunday evening, before dissipating overnight. Calm winds and prominent inverting near the surface will introduce the likelihood for some patchy fog overnight. Somewhat moistened lower levels (800mb-650mb) may introduce a slight increase in cloud cover, which may impact the development across the low-lying region. Warm and humid conditions will begin to persist throughout Monday as the recent warm front continually lifts northeast of the area by 16z. Despite the lifting warm front, moderate lower-level lapse rates and fairly unstable conditions may generate some isolated development early Monday afternoon. Mostly dry conditions are likely to exist through the remainder of this term (Monday night through Wednesday) as drier air is filtered in the mid-lower levels. This amplified pattern will begin to break down Wednesday night as the upper-level low propagates further east along the Canadian Shield.
Long Term (Thursday 10/3 through Saturday 10/5)
Upper-level ridging for SE U.S breaks down Thursday as a shortwave feature slides across the upper Great Lakes region. This flow of the Jet shifts fairly zonal through the Great Lakes, maintaining values up to 130 knots aloft. By 12z Thursday, surface convergence is likely over the eastern portion of Illinois in the relation to the present right entrance region of this jetstreak. This weak and unorganized surface low will drag its SW’ly cold front through the area by sometime Thursday evening (00z-04z Friday). Currently, the projected weak pressure and moisture gradients may hinder the intensity of this frontal passage. High pressure ~1026mb will quickly follow through for Friday and Saturday and introduce a drier and cooler airmass. Temperatures will significantly cool down near average for this time in comparison to the previous ridging pattern from short term.
