Rain Category

· With very few exceptions, this category consists of all rain events for the entire 6 hour period.

o 95%  of the total events were all rain

o 5%    of the total events rain mixed with trace frozen or freezing rain

o 75 total events

Principal forecast issues

· Significant cold air advection near the beginning of the 6 hour period may TREND the precipitation types to a rain/trace frozen mix toward the end of the 6 hour period.

· Surface wet bulb temperatures should always be used in conjunction with partial thickness to ensure that there is no shallow near ground sub-freezing layer present capable of producing freezing rain.

Vertical temperature profiles associated with rain

• Above freezing low layer (> 1312) beneath an above freezing mid layer (> 1540) characterized the soundings in the rain category
• A few freezing rain events in this category were likely characterized by a surface based and extremely shallow sub freezing layer.

Tentative findings

• Freezing rain and rain with trace frozen events in the rain category were not found to have had any significant impact upon local weather conditions. 

Footnote

• The rain category is defined on the predominant p-type nomogram by the partial thickness values of 1330/1538 - 1312/1538 – 1310/1550 – 1315/1580 – 1330/1580