NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260528_0600
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)
=== ===== === ==== ==== === === === ====
Thu 05/28 06Z 0.04 3514  83  89   7 0.00
Thu 05/28 07Z 0.05 3515  82  83   6 0.00
Thu 05/28 08Z 0.06 3517  82  78   6 0.00
Thu 05/28 09Z 0.05 3516  83  80   6 0.00
Thu 05/28 10Z 0.02 3515  83  77   6 0.00
Thu 05/28 11Z 0.03 3415  81  78   6 0.00
Thu 05/28 12Z 0.08 3415  86  85   5 0.00
Thu 05/28 13Z 0.08 3414  90  91   5 0.00
Thu 05/28 14Z 0.09 3416  90  95   4 0.00
Thu 05/28 15Z 0.08 3420  85  92   4 0.01
Thu 05/28 16Z 0.11 3420  80  81   4 0.00
Thu 05/28 17Z 0.80 3419  86  67   4 0.00
Thu 05/28 18Z 0.54 3420  88  54   3 0.00
Thu 05/28 19Z 0.56 3418  90  58   3 0.01
Thu 05/28 20Z 0.48 3319  89  63   4 0.01
Thu 05/28 21Z 0.44 3421  88  64   4 0.00
Thu 05/28 22Z 0.30 3422  91  63   4 0.00
Thu 05/28 23Z 0.18 3423  93  59   4 0.01
Fri 05/29 00Z 0.07 3425  92  46   4 0.00
Fri 05/29 01Z 0.10 3425  91  44   3 0.00
Fri 05/29 02Z 0.13 3425  93  43   3 0.00
Fri 05/29 03Z 0.20 3324  96  36   3 0.01
Fri 05/29 04Z 0.17 3423  97  34   3 0.01
Fri 05/29 05Z 0.15 3421  97  35   3 0.01
Fri 05/29 06Z 0.16 3322  98  43   3 0.01
Fri 05/29 07Z 0.20 3321  96  63   3 0.01
Fri 05/29 08Z 0.33 3323  93  78   2 0.00
Fri 05/29 09Z 0.35 3224  84  83   2 0.00
Fri 05/29 10Z 0.40 3225  75  80   2 0.00
Fri 05/29 11Z 0.41 3224  79  83   1 0.00
Fri 05/29 12Z 0.39 3221  81  82   2 0.00
Fri 05/29 13Z 0.37 3219  78  70   2 0.00
Fri 05/29 14Z 0.47 3216  74  62   2 0.00
Fri 05/29 15Z 1.74 3013  71  56   3 0.00
Fri 05/29 16Z 4.35 2711  72  61   3 0.00
Fri 05/29 17Z 7.65 2413  74  73   4 0.00
Fri 05/29 18Z 11.18 2417  67  89   5 0.00
Fri 05/29 19Z 13.64 2519  62  95   6 0.00
Fri 05/29 20Z 6.02 2622  67  94   5 0.01
Fri 05/29 21Z 1.28 2522  85  94   5 0.04
Fri 05/29 22Z 1.14 2622  90  96   4 0.09
Fri 05/29 23Z 0.79 2520  96  97   4 0.12
Sat 05/30 00Z 0.70 2418  97  95   4 0.12
Sat 05/30 01Z 0.71 2617  98  94   4 0.15
Sat 05/30 02Z 0.69 3124  91  84   2 0.10
Sat 05/30 03Z 0.44 3124  80  67   0 0.01
Sat 05/30 04Z 0.50 3122  92  74   0 0.00
Sat 05/30 05Z 0.41 3220  95  70  -1 0.01
Sat 05/30 06Z 0.16 3418  93  77   0 0.01
Sat 05/30 07Z 0.14 3521  97  85   0 0.05
Sat 05/30 08Z 0.54 0324  98  85   0 0.05
Sat 05/30 09Z 1.18 0633  99  83  -1 0.05
Sat 05/30 10Z 1.04 0533  97  92   0 0.08
Sat 05/30 11Z 0.84 0431  94  90   0 0.05
Sat 05/30 12Z 0.68 0427  81  90   0 0.02
Sat 05/30 13Z 0.69 0322  81  91  -1 0.00
Sat 05/30 14Z 2.10 0218  89  77  -2 0.00
Sat 05/30 15Z 3.27 0217  91  68  -2 0.00
Sat 05/30 16Z 3.09 0116  90  54  -2 0.00
Sat 05/30 17Z 2.77 0116  88  55  -1 0.00

Run total areal avg QPF for the Central_Greens is: 1.05 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