NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261006_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)
=== ===== === ==== ==== === === === ====
Tue 10/06 18Z 5.18 2916  81  14  -1 0.00
Tue 10/06 19Z 4.88 2918  78   6  -1 0.00
Tue 10/06 20Z 4.35 2918  78   4   0 0.00
Tue 10/06 21Z 3.83 2819  75   7   0 0.00
Tue 10/06 22Z 1.77 2920  73  15   0 0.00
Tue 10/06 23Z 1.50 2921  73  26   0 0.00
Wed 10/07 00Z 1.27 2922  69  37   0 0.00
Wed 10/07 01Z 1.02 2922  66  53   0 0.00
Wed 10/07 02Z 0.88 2922  64  56   0 0.00
Wed 10/07 03Z 0.64 2919  57  52   1 0.00
Wed 10/07 04Z 0.47 2916  50  49   1 0.00
Wed 10/07 05Z 0.45 2815  47  52   2 0.00
Wed 10/07 06Z 0.40 2814  43  53   2 0.00
Wed 10/07 07Z 0.39 2714  39  59   3 0.00
Wed 10/07 08Z 0.44 2616  38  69   3 0.00
Wed 10/07 09Z 0.41 2616  31  76   4 0.00
Wed 10/07 10Z 0.40 2517  30  80   5 0.00
Wed 10/07 11Z 0.38 2418  34  80   6 0.00
Wed 10/07 12Z 0.40 2321  37  83   7 0.00
Wed 10/07 13Z 0.41 2323  41  85   7 0.00
Wed 10/07 14Z 0.42 2226  47  84   8 0.00
Wed 10/07 15Z 0.45 2228  51  80   8 0.00
Wed 10/07 16Z 0.49 2229  51  79   8 0.00
Wed 10/07 17Z 0.54 2228  46  67   8 0.00
Wed 10/07 18Z 0.55 2225  43  63   8 0.00
Wed 10/07 19Z 0.57 2223  48  57   7 0.00
Wed 10/07 20Z 0.60 2222  59  63   7 0.00
Wed 10/07 21Z 0.61 2224  68  70   7 0.00
Wed 10/07 22Z 0.59 2225  73  79   7 0.00
Wed 10/07 23Z 0.64 2227  78  76   7 0.00
Thu 10/08 00Z 0.69 2229  82  69   7 0.00
Thu 10/08 01Z 0.70 2329  86  62   7 0.00
Thu 10/08 02Z 0.72 2329  90  61   8 0.00
Thu 10/08 03Z 0.73 2429  93  67   8 0.01
Thu 10/08 04Z 0.67 2426  94  83   8 0.02
Thu 10/08 05Z 0.62 2424  96  90   8 0.02
Thu 10/08 06Z 0.59 2323  97  96   7 0.05
Thu 10/08 07Z 0.59 2324  97  97   7 0.13
Thu 10/08 08Z 0.57 2323  97  92   8 0.12
Thu 10/08 09Z 0.55 2323  98  92   8 0.07
Thu 10/08 10Z 0.74 2424  96  94   7 0.19
Thu 10/08 11Z 0.59 2619  86  96   6 0.15
Thu 10/08 12Z 0.55 2516  84  67   6 0.03
Thu 10/08 13Z 0.70 2520  91  75   6 0.01
Thu 10/08 14Z 0.76 2620  90  90   5 0.01
Thu 10/08 15Z 0.78 2720  82  84   5 0.01
Thu 10/08 16Z 0.89 2720  78  75   5 0.01
Thu 10/08 17Z 2.22 2720  90  59   4 0.01
Thu 10/08 18Z 4.57 2620  90  51   5 0.01
Thu 10/08 19Z 8.56 2719  77  34   5 0.00
Thu 10/08 20Z 5.95 2622  82  43   4 0.02
Thu 10/08 21Z 5.13 2623  82  45   4 0.02
Thu 10/08 22Z 2.53 2623  83  39   4 0.01
Thu 10/08 23Z 1.90 2624  83  42   3 0.00
Fri 10/09 00Z 1.39 2626  89  48   3 0.00
Fri 10/09 01Z 1.34 2728  90  46   2 0.03
Fri 10/09 02Z 1.19 2827  93  38   2 0.01
Fri 10/09 03Z 1.10 2825  95  47   1 0.01
Fri 10/09 04Z 1.04 2824  96  38   1 0.02
Fri 10/09 05Z 0.98 2823  96  34   0 0.01

Run total areal avg QPF for the greens is: 0.98 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