Enhancement of the method of summer precipitation forecasting

Abstract

The physical-synoptic principles of the automated method of summer precipitation forecasting introduced into operational prognostic practice in 2006 by the decree of the Central Methodical Commission of the Federal Service for Hydrometeorology and Environmental Monitoring (Roshydromet) are presented. Beside that, improved modifications of this method, which are automatically updated, are shown. Validation of those updates based on observational data collected in 2004 has shown improvement of all major criteria of forecasts efficiency. The performed improvement is based on the more detailed quantitative realization of mechanism of various showers formation (including heavy rainfalls).

Conditions for formation and short-range forecasting of severe squalls

“…The supplementary predictor D 1 describes the increasing squall hazard, obviously, when the predictors grow above the following values: Wm > 20 m/s, V 8 > 4 m/s, 0 £ Ñ 2 p 300 £ 12 hPa/(300 km) 2 . The negative value of Ñ 2 p 300 implies no convergence of "feeding" Cb, while too high values of this quantity imply convergence exceeding the value needed for Cb cloud "feeding," when the excess generates stratiform clouds and large anvil of Cb, which hampers solar heating of the "feeding" flows in the lower layer [7,9]. The predictors D 2 and D 3 are computed as follows:…”

“…Low wind V 8 implies weak turbulence, which cannot break down organized convective updraft [9]. High humidity in the surrounding of the squall location (Ñ 2 0 T d >> 0) and dry air nearby (d 7 >> 0) can imply formation of the squall downdraft flow aloft above the front, favored by its strong cooling caused by evaporating water accumulated in the Cb cloud in the dry air [7]. Squalls develop behind the sharp front, in the air dryer than that ahead the front (Ñ 2 0 T d > 0, d 7 >> 0); the Cb cloud develops with high base because of (T 0 -T d0 ) >> 0 ahead the front.…”