Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260110_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)
=== ===== === ==== ==== === === === ====
Sat 01/10 06Z 0.99 2936  89   0  -1 0.00
Sat 01/10 07Z 0.83 3039  74   0   0 0.01
Sat 01/10 08Z 0.65 3138  57   5   0 0.00
Sat 01/10 09Z 0.54 3135  52   7   0 0.00
Sat 01/10 10Z 0.45 3133  49  11   0 0.00
Sat 01/10 11Z 0.36 3231  45  12   0 0.01
Sat 01/10 12Z 0.26 3227  42  12   0 0.01
Sat 01/10 13Z 0.17 3323  37  12   0 0.00
Sat 01/10 14Z 0.08 3419  31  12   0 0.00
Sat 01/10 15Z 0.04 3515  25  12   0 0.00
Sat 01/10 16Z 0.03 3509  22  11   1 0.00
Sat 01/10 17Z 0.02 3505  22   9   1 0.00
Sat 01/10 18Z 0.02 0001  21   7   2 0.00
Sat 01/10 19Z 0.04 1202  20   7   2 0.00
Sat 01/10 20Z 0.11 1308  20  11   2 0.00
Sat 01/10 21Z 0.20 1315  18  17   1 0.00
Sat 01/10 22Z 0.23 1421  20  34   1 0.00
Sat 01/10 23Z 0.27 1527  21  55   1 0.00
Sun 01/11 00Z 0.33 1534  22  81   0 0.00
Sun 01/11 01Z 0.46 1537  37  94  -2 0.00
Sun 01/11 02Z 0.51 1439  70  96  -1 0.03
Sun 01/11 03Z 0.48 1439  88  98   0 0.04
Sun 01/11 04Z 0.42 1440  94  98   1 0.05
Sun 01/11 05Z 0.35 1439  95  98   1 0.08
Sun 01/11 06Z 0.30 1537  96  95   0 0.06
Sun 01/11 07Z 0.19 1632  96  97  -1 0.06
Sun 01/11 08Z 0.11 1629  96  97  -1 0.06
Sun 01/11 09Z 0.04 1725  97  79  -1 0.03
Sun 01/11 10Z 0.15 1920  97  43  -2 0.02
Sun 01/11 11Z 0.31 2218  98  21  -3 0.02
Sun 01/11 12Z 0.45 2317  98  18  -4 0.02
Sun 01/11 13Z 0.55 2417  95  15  -5 0.01
Sun 01/11 14Z 0.58 2417  89  23  -6 0.01
Sun 01/11 15Z 0.65 2418  85  29  -6 0.01
Sun 01/11 16Z 0.66 2418  75  29  -7 0.00
Sun 01/11 17Z 0.94 2518  78  20  -8 0.00
Sun 01/11 18Z 2.76 2418  76  17  -9 0.00
Sun 01/11 19Z 7.19 2418  83  20 -10 0.00
Sun 01/11 20Z 5.60 2519  86  29 -10 0.00
Sun 01/11 21Z 2.61 2420  86  34 -10 0.00
Sun 01/11 22Z 1.51 2420  87  68 -10 0.00
Sun 01/11 23Z 1.03 2423  93  79 -10 0.01
Mon 01/12 00Z 1.22 2524  93  81 -10 0.03
Mon 01/12 01Z 1.17 2524  93  81 -10 0.02
Mon 01/12 02Z 1.18 2525  94  80 -10 0.02
Mon 01/12 03Z 1.30 2627  94  80 -11 0.03
Mon 01/12 04Z 1.53 2829  94  80 -11 0.04
Mon 01/12 05Z 2.02 2930  92  78 -13 0.03
Mon 01/12 06Z 1.35 2931  90  71 -14 0.03
Mon 01/12 07Z 1.25 2932  91  74 -14 0.02
Mon 01/12 08Z 1.20 2932  92  60 -15 0.02
Mon 01/12 09Z 1.01 2932  94  25 -15 0.01
Mon 01/12 10Z 0.86 2932  93  20 -14 0.01
Mon 01/12 11Z 0.65 3032  90  51 -12 0.00
Mon 01/12 12Z 0.65 3032  91  20 -12 0.00
Mon 01/12 13Z 0.61 3032  85   8 -11 0.00
Mon 01/12 14Z 0.58 2931  74   6 -11 0.00
Mon 01/12 15Z 0.57 2929  65   9 -11 0.00
Mon 01/12 16Z 0.60 2828  59  30 -10 0.00
Mon 01/12 17Z 0.63 2827  59  57 -10 0.00

Run total areal avg QPF for the greens is: 0.80 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