NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260530_0000
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)
=== ===== === ==== ==== === === === ====
Sat 05/30 00Z 0.73 2518  77  96   6 0.00
Sat 05/30 01Z 0.65 2614  83  95   6 0.16
Sat 05/30 02Z 0.39 2911  93  98   4 0.18
Sat 05/30 03Z 0.18 3319  90  91   3 0.16
Sat 05/30 04Z 0.26 3217  96  65   2 0.01
Sat 05/30 05Z 0.26 3219  96  64   2 0.01
Sat 05/30 06Z 0.19 3220  96  73   1 0.01
Sat 05/30 07Z 0.17 3518  97  90   0 0.04
Sat 05/30 08Z 0.51 0320  97  94   0 0.07
Sat 05/30 09Z 0.77 0428  98  94  -1 0.08
Sat 05/30 10Z 0.95 0433  98  92  -1 0.10
Sat 05/30 11Z 0.93 0436  98  89  -1 0.11
Sat 05/30 12Z 0.89 0436  98  90  -1 0.09
Sat 05/30 13Z 0.70 0332  97  91  -2 0.07
Sat 05/30 14Z 0.56 0329  97  91  -1 0.08
Sat 05/30 15Z 0.50 0325  92  86   0 0.06
Sat 05/30 16Z 0.56 0322  90  70   0 0.03
Sat 05/30 17Z 1.14 0119  86  62   0 0.01
Sat 05/30 18Z 1.56 0118  82  49   0 0.00
Sat 05/30 19Z 2.63 0118  78  30   0 0.00
Sat 05/30 20Z 4.12 0117  75  30   1 0.00
Sat 05/30 21Z 4.02 0116  73  37   1 0.00
Sat 05/30 22Z 2.93 0116  72  52   1 0.00
Sat 05/30 23Z 1.36 0017  70  66   1 0.00
Sun 05/31 00Z 0.64 0118  71  71   1 0.00
Sun 05/31 01Z 0.69 0120  69  58   1 0.00
Sun 05/31 02Z 0.70 0221  63  45   2 0.00
Sun 05/31 03Z 0.64 0221  59  25   2 0.00
Sun 05/31 04Z 0.58 0220  58  17   2 0.00
Sun 05/31 05Z 0.44 0218  53  15   2 0.00
Sun 05/31 06Z 0.31 0117  53  14   2 0.00
Sun 05/31 07Z 0.28 0117  54  11   3 0.00
Sun 05/31 08Z 0.18 0016  56  10   3 0.00
Sun 05/31 09Z 0.08 3515  62  16   3 0.00
Sun 05/31 10Z 0.10 3414  67  26   3 0.00
Sun 05/31 11Z 0.14 3314  67  30   3 0.00
Sun 05/31 12Z 0.17 3315  65  31   4 0.00
Sun 05/31 13Z 0.27 3213  65  37   4 0.00
Sun 05/31 14Z 0.48 3114  63  41   4 0.00
Sun 05/31 15Z 1.12 3114  61  58   5 0.00
Sun 05/31 16Z 1.70 3114  61  70   5 0.00
Sun 05/31 17Z 2.72 3114  61  74   5 0.00
Sun 05/31 18Z 3.45 3114  64  61   5 0.00
Sun 05/31 19Z 1.84 2913  75  56   5 0.01
Sun 05/31 20Z 0.97 2915  83  86   4 0.02
Sun 05/31 21Z 0.63 3017  75  83   5 0.01
Sun 05/31 22Z 0.82 3018  70  85   5 0.00
Sun 05/31 23Z 0.75 2814  77  91   4 0.01
Mon 06/01 00Z 0.60 2917  73  90   5 0.03
Mon 06/01 01Z 0.54 2916  75  76   5 0.01
Mon 06/01 02Z 0.53 2815  87  63   4 0.01
Mon 06/01 03Z 0.36 3013  85  54   5 0.01
Mon 06/01 04Z 0.23 3110  80  56   5 0.00
Mon 06/01 05Z 0.27 2807  85  51   4 0.00
Mon 06/01 06Z 0.29 2608  87  71   4 0.01
Mon 06/01 07Z 0.23 2606  87  92   4 0.03
Mon 06/01 08Z 0.17 2804  89  94   4 0.04
Mon 06/01 09Z 0.10 3104  92  95   4 0.04
Mon 06/01 10Z 0.11 3504  94  90   3 0.05
Mon 06/01 11Z 0.12 0106  95  86   3 0.06

Run total areal avg QPF for the Central_Greens is: 1.61 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