NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261028_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 10/28 12Z 0.19 2310  32  63   3 0.00
Wed 10/28 13Z 0.24 2411  34  85   3 0.00
Wed 10/28 14Z 0.24 2411  32  86   4 0.00
Wed 10/28 15Z 0.23 2411  30  86   4 0.00
Wed 10/28 16Z 0.23 2511  29  76   5 0.00
Wed 10/28 17Z 0.24 2512  30  78   6 0.00
Wed 10/28 18Z 0.23 2611  32  80   7 0.00
Wed 10/28 19Z 0.23 2611  35  84   7 0.00
Wed 10/28 20Z 0.23 2511  36  90   8 0.00
Wed 10/28 21Z 0.25 2512  39  91   8 0.00
Wed 10/28 22Z 0.27 2513  42  91   8 0.00
Wed 10/28 23Z 0.29 2514  42  89   8 0.00
Thu 10/29 00Z 0.31 2514  45  83   9 0.00
Thu 10/29 01Z 0.33 2415  49  85   9 0.00
Thu 10/29 02Z 0.34 2416  52  73   9 0.00
Thu 10/29 03Z 0.37 2417  56  68   9 0.00
Thu 10/29 04Z 0.37 2417  59  64   9 0.00
Thu 10/29 05Z 0.39 2418  63  58   9 0.00
Thu 10/29 06Z 0.41 2419  67  49   9 0.00
Thu 10/29 07Z 0.43 2420  73  35   9 0.00
Thu 10/29 08Z 0.45 2422  77  23   9 0.00
Thu 10/29 09Z 0.46 2422  81  23   9 0.00
Thu 10/29 10Z 0.47 2422  82  33   8 0.00
Thu 10/29 11Z 0.49 2422  82  39   8 0.00
Thu 10/29 12Z 0.50 2522  83  53   8 0.00
Thu 10/29 13Z 0.53 2523  84  51   8 0.00
Thu 10/29 14Z 0.54 2424  85  51   8 0.00
Thu 10/29 15Z 0.57 2424  87  51   8 0.00
Thu 10/29 16Z 0.58 2425  86  54   8 0.00
Thu 10/29 17Z 0.57 2424  82  55   8 0.00
Thu 10/29 18Z 0.57 2523  80  60   8 0.00
Thu 10/29 19Z 0.60 2524  78  55   8 0.00
Thu 10/29 20Z 0.63 2525  77  56   8 0.00
Thu 10/29 21Z 0.67 2527  75  50   9 0.00
Thu 10/29 22Z 0.71 2529  72  57  10 0.00
Thu 10/29 23Z 0.74 2531  73  83  10 0.00
Fri 10/30 00Z 0.77 2533  77  83  10 0.00
Fri 10/30 01Z 0.85 2535  78  86  10 0.00
Fri 10/30 02Z 0.97 2537  85  92   9 0.01
Fri 10/30 03Z 0.98 2637  91  87   8 0.02
Fri 10/30 04Z 0.93 2636  95  67   8 0.01
Fri 10/30 05Z 0.93 2733  97  26   7 0.02
Fri 10/30 06Z 0.95 2731  91  10   6 0.02
Fri 10/30 07Z 0.84 2729  78   8   6 0.01
Fri 10/30 08Z 0.80 2829  69   6   6 0.01
Fri 10/30 09Z 0.76 2829  63   7   5 0.00
Fri 10/30 10Z 0.73 2830  63   7   5 0.00
Fri 10/30 11Z 0.68 2829  68   5   4 0.00
Fri 10/30 12Z 0.64 2828  71   4   3 0.01
Fri 10/30 13Z 0.60 2927  75   3   2 0.01
Fri 10/30 14Z 0.59 2926  77   3   1 0.01
Fri 10/30 15Z 0.59 2924  80   2   1 0.00
Fri 10/30 16Z 0.65 2922  85   6   0 0.00
Fri 10/30 17Z 0.77 2821  87   9   0 0.00
Fri 10/30 18Z 0.96 2821  88  10   0 0.00
Fri 10/30 19Z 1.65 2923  89   9  -1 0.00
Fri 10/30 20Z 1.39 2925  90   6  -1 0.00
Fri 10/30 21Z 0.91 3026  91  12  -2 0.00
Fri 10/30 22Z 0.93 3027  93   9  -3 0.00
Fri 10/30 23Z 0.89 3028  95  11  -3 0.00

Run total areal avg QPF for the Central_Greens is: 0.13 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