NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260816_1200
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 08/16 12Z 0.04 1803  73   9  10 0.00
Sun 08/16 13Z 0.05 1805  72   9  10 0.00
Sun 08/16 14Z 0.09 1908  72  10  10 0.00
Sun 08/16 15Z 0.22 2010  75  10  10 0.00
Sun 08/16 16Z 0.41 2010  79  10  10 0.00
Sun 08/16 17Z 0.37 1910  81   9  10 0.00
Sun 08/16 18Z 0.26 1911  84   9  11 0.00
Sun 08/16 19Z 0.15 1912  87  14  12 0.00
Sun 08/16 20Z 0.15 1914  90  26  12 0.00
Sun 08/16 21Z 0.16 1916  92  41  12 0.01
Sun 08/16 22Z 0.23 2018  93  65  13 0.01
Sun 08/16 23Z 0.29 2021  94  77  13 0.01
Mon 08/17 00Z 0.30 2023  96  90  13 0.01
Mon 08/17 01Z 0.36 2025  97  91  13 0.02
Mon 08/17 02Z 0.44 2127  97  94  13 0.02
Mon 08/17 03Z 0.46 2128  97  92  14 0.02
Mon 08/17 04Z 0.47 2130  96  96  14 0.01
Mon 08/17 05Z 0.46 2132  96  96  13 0.01
Mon 08/17 06Z 0.47 2133  96  94  13 0.02
Mon 08/17 07Z 0.42 2130  96  94  13 0.02
Mon 08/17 08Z 0.44 2130  97  96  13 0.02
Mon 08/17 09Z 0.44 2227  98  96  13 0.03
Mon 08/17 10Z 0.42 2224  97  95  14 0.03
Mon 08/17 11Z 0.35 2319  97  92  14 0.02
Mon 08/17 12Z 0.29 2315  97  92  14 0.01
Mon 08/17 13Z 0.24 2313  96  91  15 0.01
Mon 08/17 14Z 0.20 2211  96  93  15 0.01
Mon 08/17 15Z 0.17 2210  96  93  15 0.01
Mon 08/17 16Z 0.16 2109  96  95  15 0.01
Mon 08/17 17Z 0.15 2208  96  93  15 0.01
Mon 08/17 18Z 0.16 2208  97  93  15 0.00
Mon 08/17 19Z 0.16 2207  98  87  15 0.00
Mon 08/17 20Z 0.17 2307  99  84  15 0.01
Mon 08/17 21Z 0.19 2407  99  69  15 0.02
Mon 08/17 22Z 0.20 2606  99  57  14 0.01
Mon 08/17 23Z 0.18 2806  99  61  14 0.02
Tue 08/18 00Z 0.20 3007  99  53  14 0.01
Tue 08/18 01Z 0.14 3208  98  33  14 0.00
Tue 08/18 02Z 0.13 3308  97  33  14 0.01
Tue 08/18 03Z 0.07 3407  96  35  14 0.00
Tue 08/18 04Z 0.05 3408  96  39  13 0.01
Tue 08/18 05Z 0.05 3508  95  23  13 0.01
Tue 08/18 06Z 0.06 3507  95  11  13 0.01
Tue 08/18 07Z 0.06 3506  94   6  13 0.00
Tue 08/18 08Z 0.06 3406  94   3  13 0.00
Tue 08/18 09Z 0.04 3505  94   2  12 0.00
Tue 08/18 10Z 0.06 3406  95   3  12 0.00
Tue 08/18 11Z 0.07 3407  95   3  12 0.00
Tue 08/18 12Z 0.07 3407  95   2  11 0.00
Tue 08/18 13Z 0.09 3307  96   2  11 0.01
Tue 08/18 14Z 0.09 3307  95   2  11 0.01
Tue 08/18 15Z 0.09 3305  94   2  11 0.01
Tue 08/18 16Z 0.14 3206  93   3  11 0.01
Tue 08/18 17Z 0.13 3206  91   3  12 0.01
Tue 08/18 18Z 0.15 3207  89   3  12 0.01
Tue 08/18 19Z 0.18 3208  88   3  12 0.00
Tue 08/18 20Z 0.16 3207  85   4  12 0.00
Tue 08/18 21Z 0.18 3207  84   4  12 0.00
Tue 08/18 22Z 0.17 3107  83   3  12 0.00
Tue 08/18 23Z 0.17 3107  83   3  12 0.00

Run total areal avg QPF for the greens is: 0.49 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1