NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260329_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 03/29 12Z 0.89 2721  85  79 -11 0.00
Sun 03/29 13Z 0.87 2621  85  68 -11 0.00
Sun 03/29 14Z 0.91 2521  84  69 -10 0.00
Sun 03/29 15Z 1.06 2519  78  69  -9 0.00
Sun 03/29 16Z 1.91 2417  67  75  -8 0.00
Sun 03/29 17Z 3.22 2317  65  77  -8 0.00
Sun 03/29 18Z 5.64 2318  65  74  -7 0.00
Sun 03/29 19Z 4.18 2320  65  72  -6 0.00
Sun 03/29 20Z 2.86 2321  65  68  -5 0.00
Sun 03/29 21Z 1.26 2322  62  65  -4 0.00
Sun 03/29 22Z 1.02 2324  61  63  -4 0.00
Sun 03/29 23Z 1.09 2425  59  58  -3 0.00
Mon 03/30 00Z 1.17 2426  59  49  -3 0.00
Mon 03/30 01Z 1.21 2427  55  55  -2 0.00
Mon 03/30 02Z 1.23 2430  55  63  -2 0.00
Mon 03/30 03Z 1.28 2431  56  69  -2 0.00
Mon 03/30 04Z 1.19 2431  59  78  -1 0.00
Mon 03/30 05Z 1.11 2431  61  81  -1 0.00
Mon 03/30 06Z 1.06 2431  66  63  -1 0.00
Mon 03/30 07Z 1.14 2330  68  51   0 0.00
Mon 03/30 08Z 0.80 2331  72  34   0 0.00
Mon 03/30 09Z 0.72 2430  73  37   0 0.00
Mon 03/30 10Z 0.77 2531  72  36   0 0.00
Mon 03/30 11Z 0.81 2529  72  37   0 0.00
Mon 03/30 12Z 0.91 2531  76  36   0 0.00
Mon 03/30 13Z 0.92 2531  79  44   0 0.00
Mon 03/30 14Z 0.91 2530  79  41   0 0.00
Mon 03/30 15Z 0.98 2529  79  45   0 0.00
Mon 03/30 16Z 1.02 2527  79  43   1 0.00
Mon 03/30 17Z 1.24 2526  80  48   1 0.00
Mon 03/30 18Z 1.70 2427  83  50   1 0.00
Mon 03/30 19Z 1.66 2529  85  60   1 0.00
Mon 03/30 20Z 1.51 2530  89  60   2 0.01
Mon 03/30 21Z 1.61 2530  90  68   2 0.01
Mon 03/30 22Z 1.50 2629  92  65   2 0.01
Mon 03/30 23Z 1.32 2629  94  64   2 0.02
Tue 03/31 00Z 1.19 2628  96  64   2 0.03
Tue 03/31 01Z 1.07 2727  97  61   2 0.03
Tue 03/31 02Z 0.94 2825  97  52   1 0.02
Tue 03/31 03Z 0.84 2823  97  51   1 0.01
Tue 03/31 04Z 0.75 2820  98  54   1 0.01
Tue 03/31 05Z 0.68 2719  98  59   1 0.01
Tue 03/31 06Z 0.61 2718  97  59   1 0.02
Tue 03/31 07Z 0.55 2717  97  64   1 0.01
Tue 03/31 08Z 0.48 2716  97  60   1 0.01
Tue 03/31 09Z 0.41 2714  98  60   1 0.01
Tue 03/31 10Z 0.34 2711  98  65   1 0.00
Tue 03/31 11Z 0.28 2610  99  62   1 0.01
Tue 03/31 12Z 0.22 2508  99  61   1 0.01
Tue 03/31 13Z 0.18 2209  98  58   2 0.00
Tue 03/31 14Z 0.13 2010  97  48   2 0.00
Tue 03/31 15Z 0.11 1913  96  55   3 0.00
Tue 03/31 16Z 0.14 1917  97  61   4 0.00
Tue 03/31 17Z 0.12 1921  98  74   4 0.01
Tue 03/31 18Z 0.08 1826  98  93   5 0.03
Tue 03/31 19Z 0.12 1929  96  96   7 0.05
Tue 03/31 20Z 0.26 2031  98  98   7 0.04
Tue 03/31 21Z 0.25 2029  94  78   9 0.04
Tue 03/31 22Z 0.31 2033  93  70  10 0.01
Tue 03/31 23Z 0.46 2138  96  57   9 0.01

Run total areal avg QPF for the greens is: 0.42 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