NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260608_1800
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)
=== ===== === ==== ==== === === === ====
Mon 06/08 18Z 0.61 3002  75   7   9 0.00
Mon 06/08 19Z 1.04 2803  76   6  10 0.00
Mon 06/08 20Z 0.92 2804  77   5  10 0.00
Mon 06/08 21Z 0.65 2604  72   5  10 0.00
Mon 06/08 22Z 0.54 2606  65   4  11 0.00
Mon 06/08 23Z 0.35 2606  61   4  11 0.00
Tue 06/09 00Z 0.38 2608  62   4  11 0.00
Tue 06/09 01Z 0.38 2608  60   4  11 0.00
Tue 06/09 02Z 0.41 2609  61   4  11 0.00
Tue 06/09 03Z 0.44 2610  62   4  11 0.00
Tue 06/09 04Z 0.50 2612  62   4  11 0.00
Tue 06/09 05Z 0.56 2613  63   4  11 0.00
Tue 06/09 06Z 0.60 2713  68   4  11 0.00
Tue 06/09 07Z 0.65 2714  72   3  11 0.00
Tue 06/09 08Z 0.62 2714  78   3  11 0.00
Tue 06/09 09Z 0.48 2813  81   3  11 0.00
Tue 06/09 10Z 0.41 2712  82   3  11 0.00
Tue 06/09 11Z 0.36 2711  83   3  11 0.00
Tue 06/09 12Z 0.26 2609  81   3  11 0.00
Tue 06/09 13Z 0.20 2408  78   3  11 0.00
Tue 06/09 14Z 0.19 2307  75   3  11 0.00
Tue 06/09 15Z 0.21 2307  72   3  11 0.00
Tue 06/09 16Z 0.30 2307  71   2  11 0.00
Tue 06/09 17Z 0.55 2407  69   2  12 0.00
Tue 06/09 18Z 0.60 2507  66   2  12 0.00
Tue 06/09 19Z 0.70 2508  68   2  12 0.00
Tue 06/09 20Z 0.53 2610  74   2  13 0.00
Tue 06/09 21Z 0.50 2511  77   1  13 0.00
Tue 06/09 22Z 0.50 2513  79   1  13 0.00
Tue 06/09 23Z 0.47 2614  82   0  14 0.00
Wed 06/10 00Z 0.46 2614  82   0  14 0.00
Wed 06/10 01Z 0.45 2714  84   1  14 0.00
Wed 06/10 02Z 0.43 2714  85   1  14 0.00
Wed 06/10 03Z 0.37 2813  85   3  14 0.00
Wed 06/10 04Z 0.31 2710  88  14  14 0.00
Wed 06/10 05Z 0.31 2710  88  22  14 0.00
Wed 06/10 06Z 0.28 2609  88  36  14 0.00
Wed 06/10 07Z 0.28 2409  89  50  14 0.00
Wed 06/10 08Z 0.25 2409  88  55  14 0.00
Wed 06/10 09Z 0.22 2308  86  53  14 0.00
Wed 06/10 10Z 0.21 2209  85  59  14 0.00
Wed 06/10 11Z 0.19 2109  82  67  14 0.00
Wed 06/10 12Z 0.20 2110  80  73  15 0.00
Wed 06/10 13Z 0.15 2011  77  77  15 0.00
Wed 06/10 14Z 0.15 2011  76  80  15 0.00
Wed 06/10 15Z 0.14 2010  76  84  15 0.00
Wed 06/10 16Z 0.15 2011  77  76  15 0.00
Wed 06/10 17Z 0.17 2011  80  61  15 0.00
Wed 06/10 18Z 0.20 1910  82  67  15 0.00
Wed 06/10 19Z 0.13 1910  83  81  15 0.00
Wed 06/10 20Z 0.11 1911  85  83  15 0.00
Wed 06/10 21Z 0.09 1812  88  85  15 0.00
Wed 06/10 22Z 0.08 1814  92  91  15 0.00
Wed 06/10 23Z 0.06 1815  94  92  15 0.01
Thu 06/11 00Z 0.09 1813  96  93  15 0.02
Thu 06/11 01Z 0.14 1913  98  94  15 0.04
Thu 06/11 02Z 0.15 1913  99  97  15 0.17
Thu 06/11 03Z 0.17 2012  98  97  15 0.20
Thu 06/11 04Z 0.18 2110  98  92  15 0.08
Thu 06/11 05Z 0.19 2209  98  91  15 0.02

Run total areal avg QPF for the greens is: 0.54 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