NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260826_0600
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)
=== ===== === ==== ==== === === === ====
Wed 08/26 06Z 0.25 3110  95  63   9 0.00
Wed 08/26 07Z 0.26 3110  92  54   9 0.00
Wed 08/26 08Z 0.21 3109  89  43   9 0.01
Wed 08/26 09Z 0.20 3108  87  37  10 0.00
Wed 08/26 10Z 0.18 3108  87  30  10 0.00
Wed 08/26 11Z 0.15 3107  88  27  10 0.00
Wed 08/26 12Z 0.11 3105  87  26  10 0.00
Wed 08/26 13Z 0.12 3005  87  26  10 0.00
Wed 08/26 14Z 0.13 2905  87  28  10 0.00
Wed 08/26 15Z 0.13 2904  86  29  10 0.00
Wed 08/26 16Z 0.11 2904  85  30  10 0.00
Wed 08/26 17Z 0.09 3003  85  29  10 0.00
Wed 08/26 18Z 0.06 3101  84  26  10 0.00
Wed 08/26 19Z 0.03 2900  84  23  11 0.00
Wed 08/26 20Z 0.03 2200  85  18  11 0.00
Wed 08/26 21Z 0.03 1700  88  15  11 0.00
Wed 08/26 22Z 0.03 1802  90  13  11 0.01
Wed 08/26 23Z 0.03 1804  90  13  11 0.00
Thu 08/27 00Z 0.03 1806  90  15  11 0.00
Thu 08/27 01Z 0.04 1707  89  15  11 0.00
Thu 08/27 02Z 0.06 1808  89  15  11 0.00
Thu 08/27 03Z 0.10 1910  86  17  11 0.00
Thu 08/27 04Z 0.14 2011  80  22  11 0.00
Thu 08/27 05Z 0.21 2112  77  24  12 0.00
Thu 08/27 06Z 0.25 2113  76  23  12 0.00
Thu 08/27 07Z 0.31 2214  77  21  12 0.00
Thu 08/27 08Z 0.37 2216  81  19  11 0.00
Thu 08/27 09Z 0.42 2217  86  19  11 0.00
Thu 08/27 10Z 0.45 2218  86  18  11 0.00
Thu 08/27 11Z 0.48 2219  84  16  11 0.00
Thu 08/27 12Z 0.53 2220  84  18  11 0.00
Thu 08/27 13Z 0.56 2220  87  21  11 0.00
Thu 08/27 14Z 0.63 2120  88  40  11 0.00
Thu 08/27 15Z 0.77 2020  84  39  11 0.00
Thu 08/27 16Z 1.92 2019  82  22  12 0.00
Thu 08/27 17Z 2.12 1919  82  34  12 0.00
Thu 08/27 18Z 1.57 1919  80  34  13 0.00
Thu 08/27 19Z 1.51 1919  79  48  13 0.00
Thu 08/27 20Z 0.60 1820  82  68  13 0.00
Thu 08/27 21Z 0.19 1821  85  72  13 0.00
Thu 08/27 22Z 0.25 1923  91  73  13 0.01
Thu 08/27 23Z 0.32 1926  91  77  13 0.01
Fri 08/28 00Z 0.43 1929  91  74  13 0.00
Fri 08/28 01Z 0.42 2029  92  64  13 0.00
Fri 08/28 02Z 0.47 2030  91  59  13 0.00
Fri 08/28 03Z 0.55 2131  93  63  13 0.02
Fri 08/28 04Z 0.54 2128  95  73  13 0.01
Fri 08/28 05Z 0.54 2227  96  80  13 0.04
Fri 08/28 06Z 0.57 2325  97  64  12 0.04
Fri 08/28 07Z 0.56 2321  98  61  12 0.02
Fri 08/28 08Z 0.51 2418  97  58  12 0.01
Fri 08/28 09Z 0.50 2416  96  50  12 0.01
Fri 08/28 10Z 0.45 2514  95  54  12 0.01
Fri 08/28 11Z 0.44 2514  96  60  12 0.01
Fri 08/28 12Z 0.42 2513  95  53  11 0.01
Fri 08/28 13Z 0.38 2511  94  39  11 0.00
Fri 08/28 14Z 0.34 2510  94  27  11 0.00
Fri 08/28 15Z 0.34 2609  93  23  11 0.00
Fri 08/28 16Z 0.36 2609  94  20  11 0.00
Fri 08/28 17Z 0.35 2608  94  20  11 0.00

Run total areal avg QPF for the greens is: 0.22 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