NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260813_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)
=== ===== === ==== ==== === === === ====
Thu 08/13 00Z 0.15 3205  84  91  12 0.00
Thu 08/13 01Z 0.16 3105  80  90  12 0.00
Thu 08/13 02Z 0.11 3103  77  79  13 0.00
Thu 08/13 03Z 0.12 2602  75  85  12 0.00
Thu 08/13 04Z 0.20 2405  79  90  12 0.00
Thu 08/13 05Z 0.21 2306  79  93  12 0.00
Thu 08/13 06Z 0.26 2307  85  96  12 0.01
Thu 08/13 07Z 0.26 2308  92  91  12 0.05
Thu 08/13 08Z 0.25 2407  92  87  12 0.03
Thu 08/13 09Z 0.24 2506  94  81  11 0.01
Thu 08/13 10Z 0.21 2606  96  89  11 0.00
Thu 08/13 11Z 0.22 2707  96  90  11 0.01
Thu 08/13 12Z 0.26 2708  96  85  11 0.01
Thu 08/13 13Z 0.24 2808  94  73  11 0.01
Thu 08/13 14Z 0.22 2907  94  60  11 0.00
Thu 08/13 15Z 0.21 3007  93  55  11 0.00
Thu 08/13 16Z 0.23 3008  88  53  11 0.00
Thu 08/13 17Z 0.33 3010  84  60  12 0.00
Thu 08/13 18Z 0.38 3111  76  63  12 0.00
Thu 08/13 19Z 0.94 3112  75  65  12 0.02
Thu 08/13 20Z 1.09 3011  79  57  12 0.01
Thu 08/13 21Z 0.90 3013  87  58  12 0.09
Thu 08/13 22Z 0.61 3014  89  54  12 0.02
Thu 08/13 23Z 0.68 3016  89  53  12 0.02
Fri 08/14 00Z 0.67 3019  85  35  12 0.02
Fri 08/14 01Z 0.63 3023  83  35  11 0.01
Fri 08/14 02Z 0.51 3124  87  37  11 0.01
Fri 08/14 03Z 0.35 3224  81  37  10 0.00
Fri 08/14 04Z 0.25 3323  77  35  10 0.00
Fri 08/14 05Z 0.25 3322  76  35  10 0.00
Fri 08/14 06Z 0.27 3221  73  36  10 0.00
Fri 08/14 07Z 0.29 3221  73  34  10 0.00
Fri 08/14 08Z 0.29 3221  72  30  10 0.00
Fri 08/14 09Z 0.30 3221  75  24   9 0.00
Fri 08/14 10Z 0.35 3122  75  21   9 0.00
Fri 08/14 11Z 0.33 3222  74  18   9 0.00
Fri 08/14 12Z 0.34 3122  77  23   9 0.00
Fri 08/14 13Z 0.32 3222  77  27   9 0.00
Fri 08/14 14Z 0.32 3221  76  32   9 0.00
Fri 08/14 15Z 0.34 3219  74  31   9 0.00
Fri 08/14 16Z 0.37 3218  70  38   9 0.00
Fri 08/14 17Z 0.43 3217  71  37   9 0.00
Fri 08/14 18Z 0.75 3116  76  39   9 0.00
Fri 08/14 19Z 1.44 3015  79  43   9 0.00
Fri 08/14 20Z 1.72 3014  79  44   9 0.00
Fri 08/14 21Z 1.28 2915  77  41  10 0.00
Fri 08/14 22Z 0.79 3015  75  42  10 0.00
Fri 08/14 23Z 0.60 3117  73  43  10 0.00
Sat 08/15 00Z 0.47 3218  71  48   9 0.00
Sat 08/15 01Z 0.37 3220  70  58   9 0.00
Sat 08/15 02Z 0.27 3320  68  58   9 0.00
Sat 08/15 03Z 0.23 3320  68  34   9 0.00
Sat 08/15 04Z 0.15 3319  72  29   9 0.00
Sat 08/15 05Z 0.08 3418  73  28   8 0.00
Sat 08/15 06Z 0.06 3418  73  25   8 0.00
Sat 08/15 07Z 0.03 3418  67  19   9 0.00
Sat 08/15 08Z 0.02 3417  63  17   9 0.00
Sat 08/15 09Z 0.03 3416  61  17   9 0.00
Sat 08/15 10Z 0.02 3516  55  17   9 0.00
Sat 08/15 11Z 0.02 3516  51  18   9 0.00

Run total areal avg QPF for the Central_Greens is: 0.33 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