NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260708_0000
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 07/08 00Z 0.21 1206  77  58  13 0.00
Wed 07/08 01Z 0.20 1206  78  51  13 0.00
Wed 07/08 02Z 0.15 1204  77  45  13 0.00
Wed 07/08 03Z 0.10 1102  75  43  13 0.00
Wed 07/08 04Z 0.10 0901  73  39  13 0.00
Wed 07/08 05Z 0.09 0702  71  34  13 0.00
Wed 07/08 06Z 0.09 0101  71  30  13 0.00
Wed 07/08 07Z 0.08 3202  72  25  13 0.00
Wed 07/08 08Z 0.10 3103  74  21  13 0.00
Wed 07/08 09Z 0.13 3205  76  15  13 0.00
Wed 07/08 10Z 0.14 3205  80  15  12 0.00
Wed 07/08 11Z 0.11 3305  81  20  12 0.00
Wed 07/08 12Z 0.08 3305  82  21  12 0.00
Wed 07/08 13Z 0.09 3304  84  12  12 0.00
Wed 07/08 14Z 0.17 3206  87   7  12 0.00
Wed 07/08 15Z 0.16 3105  88   5  13 0.00
Wed 07/08 16Z 0.16 3003  87   6  13 0.00
Wed 07/08 17Z 0.36 2803  87   9  13 0.00
Wed 07/08 18Z 0.55 2704  84  10  13 0.00
Wed 07/08 19Z 0.86 2604  81  13  14 0.00
Wed 07/08 20Z 1.04 2506  81  16  14 0.00
Wed 07/08 21Z 0.93 2508  82  13  14 0.00
Wed 07/08 22Z 0.74 2510  85  11  14 0.00
Wed 07/08 23Z 0.56 2511  86  11  14 0.00
Thu 07/09 00Z 0.53 2513  82  13  15 0.00
Thu 07/09 01Z 0.54 2614  81  12  15 0.00
Thu 07/09 02Z 0.58 2616  80  11  15 0.00
Thu 07/09 03Z 0.66 2619  77   9  15 0.00
Thu 07/09 04Z 0.77 2621  83  12  15 0.00
Thu 07/09 05Z 0.81 2621  83  13  15 0.00
Thu 07/09 06Z 0.85 2722  85  19  14 0.00
Thu 07/09 07Z 0.87 2722  87  24  14 0.00
Thu 07/09 08Z 0.83 2722  91  36  14 0.00
Thu 07/09 09Z 0.74 2721  90  32  14 0.01
Thu 07/09 10Z 0.66 2819  90  35  14 0.01
Thu 07/09 11Z 0.54 2817  89  36  14 0.02
Thu 07/09 12Z 0.44 2815  87  31  15 0.01
Thu 07/09 13Z 0.35 2811  85  27  15 0.01
Thu 07/09 14Z 0.32 2609  84  28  15 0.01
Thu 07/09 15Z 0.31 2509  83  43  15 0.00
Thu 07/09 16Z 0.36 2410  83  38  15 0.00
Thu 07/09 17Z 0.53 2411  83  51  15 0.00
Thu 07/09 18Z 0.67 2411  82  62  16 0.00
Thu 07/09 19Z 0.92 2312  85  66  16 0.00
Thu 07/09 20Z 0.68 2311  88  60  16 0.00
Thu 07/09 21Z 0.49 2312  87  58  16 0.01
Thu 07/09 22Z 0.62 2414  87  56  16 0.03
Thu 07/09 23Z 0.68 2516  87  51  16 0.01
Fri 07/10 00Z 0.67 2616  90  48  16 0.01
Fri 07/10 01Z 0.70 2617  90  41  16 0.02
Fri 07/10 02Z 0.69 2717  91  39  15 0.02
Fri 07/10 03Z 0.66 2718  93  47  15 0.04
Fri 07/10 04Z 0.59 2818  93  50  15 0.03
Fri 07/10 05Z 0.56 2817  95  62  14 0.06
Fri 07/10 06Z 0.52 2817  94  83  14 0.05
Fri 07/10 07Z 0.44 2815  94  83  14 0.01
Fri 07/10 08Z 0.42 2814  96  85  14 0.01
Fri 07/10 09Z 0.41 2913  98  84  14 0.02
Fri 07/10 10Z 0.33 2911  97  85  13 0.02
Fri 07/10 11Z 0.31 3010  96  83  13 0.03

Run total areal avg QPF for the greens is: 0.44 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