Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260222_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)
=== ===== === ==== ==== === === === ====
Sun 02/22 06Z 0.11 1510  95  45  -8 0.00
Sun 02/22 07Z 0.13 1512  93  49  -8 0.00
Sun 02/22 08Z 0.10 1513  90  54  -8 0.00
Sun 02/22 09Z 0.08 1513  87  62  -8 0.00
Sun 02/22 10Z 0.07 1513  86  68  -8 0.00
Sun 02/22 11Z 0.06 1513  86  79  -8 0.00
Sun 02/22 12Z 0.06 1513  86  89  -8 0.00
Sun 02/22 13Z 0.09 1512  86  91  -8 0.00
Sun 02/22 14Z 0.12 1412  85  94  -8 0.00
Sun 02/22 15Z 0.15 1412  84  94  -8 0.00
Sun 02/22 16Z 0.21 1313  83  91  -8 0.00
Sun 02/22 17Z 0.25 1313  83  93  -8 0.00
Sun 02/22 18Z 0.29 1314  79  95  -8 0.00
Sun 02/22 19Z 0.33 1314  71  90  -8 0.00
Sun 02/22 20Z 0.34 1214  69  89  -8 0.00
Sun 02/22 21Z 0.40 1114  71  86  -8 0.00
Sun 02/22 22Z 0.46 1016  71  86  -8 0.00
Sun 02/22 23Z 0.56 1019  72  87  -8 0.00
Mon 02/23 00Z 0.61 1022  72  87  -8 0.00
Mon 02/23 01Z 0.61 0922  71  81  -8 0.00
Mon 02/23 02Z 0.64 1023  74  73  -8 0.00
Mon 02/23 03Z 0.70 0925  77  83  -8 0.00
Mon 02/23 04Z 0.78 0826  79  75  -8 0.00
Mon 02/23 05Z 0.81 0826  81  77  -9 0.00
Mon 02/23 06Z 0.82 0825  82  85  -9 0.01
Mon 02/23 07Z 0.84 0726  87  85  -9 0.03
Mon 02/23 08Z 0.80 0627  86  85  -9 0.05
Mon 02/23 09Z 0.88 0630  88  86 -10 0.05
Mon 02/23 10Z 0.92 0531  89  85 -10 0.05
Mon 02/23 11Z 0.91 0534  90  86 -10 0.03
Mon 02/23 12Z 0.89 0434  74  85 -10 0.02
Mon 02/23 13Z 0.98 0435  72  85 -11 0.01
Mon 02/23 14Z 0.82 0433  83  86 -11 0.01
Mon 02/23 15Z 0.75 0332  90  85 -11 0.07
Mon 02/23 16Z 0.72 0332  90  85 -11 0.09
Mon 02/23 17Z 0.59 0232  91  85 -11 0.07
Mon 02/23 18Z 0.48 0133  91  86 -11 0.05
Mon 02/23 19Z 0.37 0134  91  86 -11 0.04
Mon 02/23 20Z 0.28 0035  92  85 -10 0.03
Mon 02/23 21Z 0.18 0035  92  85 -10 0.02
Mon 02/23 22Z 0.13 3535  91  86 -10 0.02
Mon 02/23 23Z 0.10 3536  92  85 -11 0.02
Tue 02/24 00Z 0.09 3536  92  86 -12 0.01
Tue 02/24 01Z 0.13 3537  91  86 -12 0.01
Tue 02/24 02Z 0.11 3536  90  85 -13 0.01
Tue 02/24 03Z 0.09 3534  90  85 -13 0.01
Tue 02/24 04Z 0.13 3432  92  81 -13 0.00
Tue 02/24 05Z 0.25 3330  91  76 -13 0.00
Tue 02/24 06Z 0.25 3330  90  75 -14 0.01
Tue 02/24 07Z 0.20 3330  91  73 -14 0.01
Tue 02/24 08Z 0.41 3329  96  80 -15 0.01
Tue 02/24 09Z 0.44 3227  95  82 -15 0.01
Tue 02/24 10Z 0.28 3226  90  74 -15 0.01
Tue 02/24 11Z 0.27 3224  90  71 -15 0.00
Tue 02/24 12Z 0.28 3124  89  76 -15 0.00
Tue 02/24 13Z 0.27 3124  88  54 -15 0.00
Tue 02/24 14Z 0.27 3123  86  34 -15 0.00
Tue 02/24 15Z 0.26 3122  85  34 -15 0.00
Tue 02/24 16Z 0.31 3121  86  52 -15 0.00
Tue 02/24 17Z 0.33 3019  86  70 -15 0.00

Run total areal avg QPF for the Central_Greens is: 0.76 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