NAM3 EXPERIMENTAL Froude Number for the Northern Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20260528_1200
Using the MB925 to MB850 layer.
Assumes Northern_Greens are orthogonal to 290 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Northern_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 05/28 12Z 0.23 3513  94  76   4 0.00
Thu 05/28 13Z 0.33 3416  95  78   4 0.00
Thu 05/28 14Z 0.45 3316  95  77   3 0.00
Thu 05/28 15Z 0.62 3317  94  69   3 0.00
Thu 05/28 16Z 0.88 3318  94  68   3 0.01
Thu 05/28 17Z 1.04 3318  95  69   3 0.01
Thu 05/28 18Z 0.91 3319  96  70   3 0.01
Thu 05/28 19Z 0.88 3319  94  71   3 0.01
Thu 05/28 20Z 0.67 3216  98  74   4 0.03
Thu 05/28 21Z 0.84 3321  93  57   4 0.09
Thu 05/28 22Z 0.71 3423  96  66   4 0.02
Thu 05/28 23Z 0.58 3524  93  60   3 0.02
Fri 05/29 00Z 0.48 3524  93  53   3 0.01
Fri 05/29 01Z 0.51 3524  91  54   3 0.00
Fri 05/29 02Z 0.51 3523  88  54   2 0.00
Fri 05/29 03Z 0.55 3422  92  41   2 0.00
Fri 05/29 04Z 0.58 3421  91  38   2 0.00
Fri 05/29 05Z 0.59 3420  90  41   2 0.00
Fri 05/29 06Z 0.74 3219  94  55   2 0.00
Fri 05/29 07Z 0.87 3120  96  81   2 0.01
Fri 05/29 08Z 0.80 3222  90  93   2 0.01
Fri 05/29 09Z 0.74 3224  77  91   2 0.00
Fri 05/29 10Z 0.72 3324  72  84   1 0.00
Fri 05/29 11Z 0.72 3323  72  89   1 0.00
Fri 05/29 12Z 0.74 3220  71  83   1 0.00
Fri 05/29 13Z 0.79 3217  78  78   1 0.00
Fri 05/29 14Z 1.42 3114  82  77   1 0.00
Fri 05/29 15Z 3.10 3012  79  79   2 0.00
Fri 05/29 16Z 4.40 2909  76  77   3 0.00
Fri 05/29 17Z 4.06 2708  70  80   4 0.00
Fri 05/29 18Z 3.73 2507  68  86   5 0.00
Fri 05/29 19Z 1.51 2307  71  97   5 0.00
Fri 05/29 20Z 0.75 2312  80  94   5 0.02
Fri 05/29 21Z 0.34 2213  80  92   5 0.02
Fri 05/29 22Z 0.22 2116  82  93   5 0.01
Fri 05/29 23Z 0.22 2118  94  93   5 0.06
Sat 05/30 00Z 0.36 2117  98  99   5 0.16
Sat 05/30 01Z 0.86 2713  98  98   3 0.31
Sat 05/30 02Z 0.73 2920  98  99   2 0.17
Sat 05/30 03Z 0.59 2917  90  87   0 0.08
Sat 05/30 04Z 0.44 3014  92  83   0 0.06
Sat 05/30 05Z 0.18 3308  93  89   0 0.08
Sat 05/30 06Z 0.12 0209  97  94   0 0.12
Sat 05/30 07Z 0.36 0620  99  93   0 0.13
Sat 05/30 08Z 0.83 0729  98  93   0 0.11
Sat 05/30 09Z 0.98 0832  97  92   0 0.07
Sat 05/30 10Z 0.77 0729  94  89   0 0.04
Sat 05/30 11Z 0.53 0626  88  88   0 0.02
Sat 05/30 12Z 0.39 0522  80  80   0 0.00
Sat 05/30 13Z 0.33 0519  75  65   0 0.00
Sat 05/30 14Z 0.36 0516  84  57  -1 0.00
Sat 05/30 15Z 0.49 0514  89  57  -1 0.00
Sat 05/30 16Z 0.44 0415  89  59  -1 0.00
Sat 05/30 17Z 0.98 0316  86  68  -1 0.00
Sat 05/30 18Z 1.98 0316  83  76   0 0.00
Sat 05/30 19Z 1.79 0216  78  84   0 0.00
Sat 05/30 20Z 0.74 0215  74  84   0 0.00
Sat 05/30 21Z 0.27 0116  72  82   1 0.00
Sat 05/30 22Z 0.32 0116  71  83   1 0.00
Sat 05/30 23Z 0.27 0216  65  80   1 0.00

Run total areal avg QPF for the Northern_Greens is: 1.69 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