NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260528_0600
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)
=== ===== === ==== ==== === === === ====
Thu 05/28 06Z 0.06 3514  82  88   6 0.00
Thu 05/28 07Z 0.08 3515  83  81   6 0.00
Thu 05/28 08Z 0.06 3516  83  78   6 0.00
Thu 05/28 09Z 0.07 3515  83  76   6 0.00
Thu 05/28 10Z 0.08 3515  83  73   6 0.00
Thu 05/28 11Z 0.12 3415  83  79   5 0.00
Thu 05/28 12Z 0.16 3416  87  86   5 0.00
Thu 05/28 13Z 0.16 3415  89  88   4 0.00
Thu 05/28 14Z 0.17 3417  90  89   4 0.00
Thu 05/28 15Z 0.20 3419  88  83   3 0.01
Thu 05/28 16Z 0.30 3420  86  73   3 0.01
Thu 05/28 17Z 1.20 3419  90  65   3 0.01
Thu 05/28 18Z 0.99 3419  91  60   3 0.01
Thu 05/28 19Z 1.07 3319  92  67   4 0.02
Thu 05/28 20Z 0.79 3420  91  64   4 0.02
Thu 05/28 21Z 0.65 3421  90  62   4 0.01
Thu 05/28 22Z 0.48 3421  92  61   4 0.01
Thu 05/28 23Z 0.37 3423  93  56   3 0.01
Fri 05/29 00Z 0.30 3424  92  48   3 0.00
Fri 05/29 01Z 0.34 3424  93  46   3 0.00
Fri 05/29 02Z 0.31 3424  93  45   3 0.00
Fri 05/29 03Z 0.33 3424  94  40   3 0.01
Fri 05/29 04Z 0.32 3423  96  38   3 0.01
Fri 05/29 05Z 0.34 3322  97  41   3 0.01
Fri 05/29 06Z 0.37 3322  98  50   3 0.02
Fri 05/29 07Z 0.39 3322  96  74   2 0.01
Fri 05/29 08Z 0.51 3323  91  84   2 0.00
Fri 05/29 09Z 0.57 3224  84  85   1 0.00
Fri 05/29 10Z 0.57 3225  77  83   1 0.00
Fri 05/29 11Z 0.54 3224  81  81   1 0.00
Fri 05/29 12Z 0.50 3221  81  78   1 0.00
Fri 05/29 13Z 0.46 3219  79  68   2 0.00
Fri 05/29 14Z 0.52 3216  74  59   2 0.00
Fri 05/29 15Z 1.50 3012  70  56   3 0.00
Fri 05/29 16Z 3.53 2710  70  67   3 0.00
Fri 05/29 17Z 5.70 2412  71  77   4 0.00
Fri 05/29 18Z 7.94 2416  67  92   5 0.00
Fri 05/29 19Z 10.32 2418  63  96   6 0.00
Fri 05/29 20Z 4.31 2522  75  95   5 0.03
Fri 05/29 21Z 1.23 2523  86  95   4 0.06
Fri 05/29 22Z 1.06 2523  92  97   3 0.09
Fri 05/29 23Z 0.73 2520  97  96   4 0.13
Sat 05/30 00Z 0.66 2518  97  85   4 0.10
Sat 05/30 01Z 0.73 2717  97  86   3 0.12
Sat 05/30 02Z 0.68 3022  90  81   1 0.07
Sat 05/30 03Z 0.49 3121  82  69   1 0.01
Sat 05/30 04Z 0.44 3118  91  79   0 0.01
Sat 05/30 05Z 0.37 3317  95  79   0 0.03
Sat 05/30 06Z 0.37 0016  95  83   0 0.07
Sat 05/30 07Z 0.51 0321  97  88   0 0.08
Sat 05/30 08Z 0.82 0528  98  88   0 0.07
Sat 05/30 09Z 1.10 0633  97  85   0 0.05
Sat 05/30 10Z 0.88 0532  93  91   0 0.06
Sat 05/30 11Z 0.68 0429  85  88   0 0.03
Sat 05/30 12Z 0.57 0426  80  79   0 0.01
Sat 05/30 13Z 0.59 0422  83  76  -1 0.00
Sat 05/30 14Z 1.36 0319  90  69  -2 0.00
Sat 05/30 15Z 1.90 0217  90  67  -2 0.00
Sat 05/30 16Z 2.85 0216  88  64  -2 0.00
Sat 05/30 17Z 2.84 0116  85  66  -1 0.00

Run total areal avg QPF for the greens is: 1.19 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