NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260913_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)
=== ===== === ==== ==== === === === ====
Sun 09/13 06Z 0.45 2226  95  99  13 0.00
Sun 09/13 07Z 0.49 2228  97  96  14 0.06
Sun 09/13 08Z 0.45 2224  96  89  14 0.09
Sun 09/13 09Z 0.50 2228  98  88  14 0.23
Sun 09/13 10Z 0.49 2227  98  93  14 0.14
Sun 09/13 11Z 0.55 2327  98  93  14 0.17
Sun 09/13 12Z 0.50 2324  97  90  13 0.13
Sun 09/13 13Z 0.46 2323  97  77  13 0.08
Sun 09/13 14Z 0.42 2222  98  73  13 0.06
Sun 09/13 15Z 0.42 2320  98  56  13 0.05
Sun 09/13 16Z 0.38 2316  96  53  14 0.02
Sun 09/13 17Z 0.36 2414  94  53  14 0.01
Sun 09/13 18Z 0.32 2412  91  51  14 0.00
Sun 09/13 19Z 0.34 2411  90  54  14 0.00
Sun 09/13 20Z 0.30 2409  86  52  15 0.00
Sun 09/13 21Z 0.25 2408  84  37  15 0.00
Sun 09/13 22Z 0.38 2511  86  42  15 0.00
Sun 09/13 23Z 0.45 2514  90  53  14 0.01
Mon 09/14 00Z 0.52 2516  94  67  14 0.03
Mon 09/14 01Z 0.59 2517  95  67  14 0.03
Mon 09/14 02Z 0.78 2622  94  68  14 0.12
Mon 09/14 03Z 0.96 2725  94  61  13 0.12
Mon 09/14 04Z 1.18 2826  95  60  12 0.04
Mon 09/14 05Z 1.01 2926  95  63  10 0.03
Mon 09/14 06Z 0.72 3024  90  62  10 0.02
Mon 09/14 07Z 0.74 3024  88  75   9 0.01
Mon 09/14 08Z 0.78 3023  86  83   8 0.01
Mon 09/14 09Z 0.84 2924  92  52   7 0.01
Mon 09/14 10Z 0.87 3026  95  31   6 0.01
Mon 09/14 11Z 0.76 3128  95  21   5 0.02
Mon 09/14 12Z 0.56 3226  92  18   5 0.01
Mon 09/14 13Z 0.46 3224  91  19   5 0.01
Mon 09/14 14Z 0.41 3223  89  17   5 0.02
Mon 09/14 15Z 0.39 3221  87  13   5 0.01
Mon 09/14 16Z 0.39 3220  85  10   5 0.01
Mon 09/14 17Z 0.47 3219  84   6   4 0.00
Mon 09/14 18Z 0.55 3219  84   5   4 0.00
Mon 09/14 19Z 0.92 3219  82   6   4 0.00
Mon 09/14 20Z 1.04 3218  83  10   4 0.00
Mon 09/14 21Z 0.72 3218  80  16   4 0.00
Mon 09/14 22Z 0.58 3220  79  19   4 0.00
Mon 09/14 23Z 0.55 3321  81  20   4 0.00
Tue 09/15 00Z 0.41 3320  82  19   4 0.00
Tue 09/15 01Z 0.28 3420  81  17   4 0.00
Tue 09/15 02Z 0.18 3419  77  15   5 0.00
Tue 09/15 03Z 0.09 3417  71  13   6 0.00
Tue 09/15 04Z 0.04 3514  65  11   7 0.00
Tue 09/15 05Z 0.05 0011  59   9   8 0.00
Tue 09/15 06Z 0.02 3509  60   8   8 0.00
Tue 09/15 07Z 0.04 0106  56   7   8 0.00
Tue 09/15 08Z 0.04 3403  51   6   8 0.00
Tue 09/15 09Z 0.03 3301  47   6   9 0.00
Tue 09/15 10Z 0.03 0201  47   6   8 0.00
Tue 09/15 11Z 0.02 1900  45   5   8 0.00
Tue 09/15 12Z 0.04 1903  44   4   8 0.00
Tue 09/15 13Z 0.04 1904  43   3   8 0.00
Tue 09/15 14Z 0.06 2105  43   3   9 0.00
Tue 09/15 15Z 0.09 2205  46   3   9 0.00
Tue 09/15 16Z 0.08 2105  45   3  10 0.00
Tue 09/15 17Z 0.06 2006  46   3  11 0.00

Run total areal avg QPF for the greens is: 1.56 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